Disclaimer: Shonda owns it. I just borrow the characters for fun. Ed Sheeran owns the lyrics to the song used in the title, called "Small Bump."

This picks up after 9x18, "Idle Hands." More MerDer, because I can never get enough of them. Spoilery if you haven't seen the episode yet. Enjoy!

The kicks start up again around midnight, just when Meredith's slipping into a deep sleep. She opens her eyes and rolls onto her back, nearly whomping Derek with the basketball belly as she shifts positions. Her fingers gently trail over the front of Derek's t-shirt that she's wearing, hoping to settle one child down, so she can get a few hours of sleep before the child down the hall wakes them up at the crack of dawn.

"You know, for an eggplant-sized human that weighs two and a half pounds, you've got a lot of power in those feet," Meredith whispers in a soft voice. He kicks right into the palm of her hand with what she assumes is his heel, as though he's communicating with her from the inside.

Meredith looks down at her belly and smiles. "Daddy and I got to see you earlier today. I swear, every time I see you, I love you more and more. Daddy said you look like me. I actually think you look like him. We'll have to ask your big sister to break the tie," she says.

"Sorry for yelling at you about the kicking, by the way. I know you're just trying to get more comfortable in there, and my ribcage kind of prevents that. But you've still got twelve weeks' worth of growing to do in there, and I want you have every minute of it, so if that means you have to kick, I can deal with it," Meredith tells him.

She thinks of what life will be like twelve weeks from now, having a two year old daughter and a newborn son. Irrational mommy panic washes over her, and she opens the nightstand drawer next to her out of habit. She pulls the emergency stash of Peeps from inside and sets the pack of purple ducks on her belly.

Derek hears the plastic crinkle as she rips it off, and he peeks open his eyes. "What're you doing?" he asks, his voice thick with sleep.

Meredith bites the head off an innocent marshmallow duck, chomping on it anxiously. "Eating Peeps in the dark, and wondering what we're gonna do when Zola's covered in finger paint, and Adam's covered in poop, and then we both get covered in finger paint and poop, and before you know it, this house descends into chaos."

Derek rubs the sleep from his eyes as he sits up, trying to make sense of his wife's ramble. "What? Who's Adam?"

"The baby. I'm testing it out," Meredith explains. "Peep?"

"I'm good; thanks," Derek chuckles, grabbing a notepad and pen off his nightstand, then switching on the lamp. "I like Adam, though. That's going on the list."

"Ouch," Meredith winces when he kicks again. "Are you wide awake in there, little guy?"

Derek smiles at the way she greets their son, and he spreads his palm over her shirt. "You realize that feeding him sugar-covered marshmallows is only gonna make him more hyper, right?"

"Damn. Didn't think of that."

"And as far as finger paint and poop go, there's no one I'd rather be covered in it with than you," Derek says before kissing her. "Hey, what about Jack?"

Meredith rolls her eyes playfully. "Jack Shepherd? Everyone would think we're LOST junkies."

"I just wanted to see if you got the reference. Gotta say, I'm impressed," Derek compliments. He leans down and presses a kiss to Meredith's belly. "Daddy loves you so much, buddy," he tells his son.

"Are you happy it's a boy?" she asks.

"There were days when I thought we'd never have one baby. Now we have one of each, and they're both perfect. I couldn't be more thrilled," Derek says with sincerity.

"Me, either." She swaps out the Peeps for the newest stack of ultrasound pictures, ones that they've already flipped through a hundred times, but could stare at all day.

Derek grins at the picture on top of the pile. "Definitely not an eleventh finger. He is all boy. God, I wish Mark could see this. He'd be a proud uncle. Probably frame this on his wall."

Meredith smiles, trailing her hand across Derek's thigh. "It's a very impressive penis. Like father, like son."

"Are you feeling me up?"

"I can't help it. I've been thinking of going to the carnival all day," Meredith says, her fingers working their way to his groin. It doesn't take long for him to decode what carnival means when she swings a leg over either side of him. "Take me for a ride, Derek."

He's happy to take that ride with her, especially when she pulls her shirt over her head. "Yes, dear."

...

It's not the kicks that wake Meredith up the next morning. It's the heartburn. She forces herself to shuffle out of bed anyway, because she knows Zola's up by now. Her limbs are sated and sore from the night before, but she still wouldn't trade the many rounds of carnival rides for anything.

After she empties her bladder that's becoming progressively more squished each day, she goes downstairs, following the sound of Zola's laughter into the playroom. Meredith stands in the doorway and watches her husband and daughter, who are engrossed in a conversation about the Easter bunny during their morning tea party.

Zola's eyes light up when she sees Meredith, and she quickly runs over her. "Mommy!"

"Hey, Zo. Are you having tea with Daddy?" Meredith asks.

"Uh huh." Zola grabs Meredith's hand and pulls her toward the pink table. "I get you some."

"Thank you, Lovebug," Meredith says as she maneuvers herself into the small chair that clearly wasn't designed for pregnant women.

Derek puts a pretend scoop of sugar in his teacup and takes a pretend sip. "You could've slept in. I know you were... worn out after last night."

"Heartburn again. He better come out with a head full of your hair, or I'll have suffered months on end for nothing," she replies.

"He?" Zola echoes.

Meredith bites her lip when she realizes she inadvertently spilled the beans, but decides to roll with it. They were going to tell her eventually, and now's as good a time as any. "Yeah. Our baby's a 'he,' Zozo. Isn't that cool?"

"I gettin' a baby brother?" Zola asks excitedly.

"Yeah. Mommy and I saw him last night. He's getting really big now. He can't wait to come out and meet you," Derek says, pulling her onto his lap.

Zola looks up at Derek, her tiny mouth agape. "Can I see him?"

"Sure you can." Meredith pulls the stack of photos from the pocket of her robe, and hands one to Zola. "There he is, Zo. See his little face?"

Zola studies the picture in fascination, tracing her tiny finger over the baby's profile. "And I can play with him?"

"You're his big sister. It's your job to play with him. And you can hold him, and tell him stories, and change his smelly diapers," Derek chuckles as he bounces her on his knee.

"Eww!" Zola shrieks as Meredith hands her another sonogram picture. She points between the baby's legs, and what comes out of her mouth next is something neither of them expected. "Is that his penis?"

Derek looks down at his two year old, at a loss for words. Meredith recovers first, and simply nods in concurrence. "Yes, it is. Very good, Zo."

"How do you know that word?" Derek asks.

"Ryan taught me it," Zola shrugs, as though the explanation is obvious.

"Ryan is the urologist's son. He and Zola hang out at daycare," Meredith clarifies. She feels the baby doing his usual morning stretches and smiles, thankful for the opportunity to change the subject. "Zo, your brother's awake."

Zola hops off Derek's lap to kiss Meredith's belly, like she did multiple times a day. "Good morning," she greets him. "What's his name gonna be?"

"We don't know yet. What do you think his name should be?" Meredith asks her.

"Umm..." Zola considers seriously before speaking. "Aladdin."

"Aladdin Shepherd. It's catchy. We'll throw it into the mix," Derek jokes.

"When you come out, you can play dress up with me and Sofia, and we can have tea parties," Zola says to Meredith's bump.

Derek notices that Meredith is biting her lip, unwilling to break the news to Zola that when the baby is old enough to participate in such activities, he may not be so keen on sipping pretend tea while being forced to wear a princess costume, so he pats her shoulder in reassurance.

"Don't worry. My sisters made me do all that stuff, too, and I'm a catch," Derek says with feigned arrogance. "Our son will be in good hands with a big sister like Zo."

"Is he gonna sleep in my room?"

"He'll sleep with me and Daddy for a while, so I can feed him during the night, but once he's a little older, he'll sleep in the room next to yours," Meredith explains.

Zola cocks her head in the same way her dad does. "But there's no stuff in there."

"Pretty soon, we're gonna paint it, then put his crib in there, and a changing table, and a rocking chair," Derek lists.

"Can I sing him the Itsy Bitsy Spider song?" Zola asks as she rubs small circles over her mom's belly.

Meredith presses a kiss to the top of Zola's head, breathing in the scent of her fruity shampoo. "Of course you can," she says.

Zola gasps slightly when she feels something against her hand, and her mouth forms a tiny 'o' shape. "He kicked me!"

"That means he's excited to meet you. I think he's doing cartwheels in there," Meredith laughs.

"Hey, Zozo. How about we call grandma later, so you can tell her about your brother?" Derek suggests, both of them proud that she's so inquisitive and wants to be included in all the baby prep.

"'Cause I'm his only big sister forever and ever?" Zola says with her cheek pressed to Meredith's belly.

Meredith smiles at her daughter. "Forever and ever, Zo."

...

Zola's been Skyping weekly with her grandma for nearly a year, so it's no surprise when they find her on the couch with Meredith's iPad after lunch, already chatting away with her.

"Daddy said the Easter bunny is comin' soon, and that I gotta leave him carrots to eat," Zola says.

"Bunnies love carrots, so I'm sure the Easter bunny will appreciate his snack," comes Carolyn's voice from the other side of the screen.

Derek peeks over the couch in suspicion after he and Meredith walk into the living room. "Hey, Ma. We didn't know she called you already. How long have you guys been talking?" he asks in amusement, sitting on one side of Zola while Meredith sits on the other.

"She called a few minutes ago, and said you two were finishing lunch. How are you doing?" Carolyn asks, nearly losing her breath when Meredith's belly comes into focus. "Oh, sweetheart, look at you."

Meredith laughs in spite of herself. "I know. I'm a beached whale."

"No, you look beautiful. Pregnancy agrees with you," Carolyn refutes. "How's my grandbaby in there?"

"That's actually why we called. We have some news. Right, Zo?" Derek prompts, handing Zola the telltale ultrasound picture.

Zola proudly holds it up to the screen. "I'm gettin' a brother!" she exclaims.

Before Carolyn has the chance to say anything, Derek can already see the tears in his mom's eyes. It's the look he always wondered if he'd get to see on her face, the one that said my son is having his own little son. And now that he's seen it, it's worth everything.

"It's a boy," Carolyn says in awe as she admires the picture Zola is holding. "Oh, would you look at that face."

"He has a penis, grandma!" Zola adds with exuberance, pointing out said body part on the photo.

"Yes, you're right. He does," Carolyn agrees, trying to bite back a laugh at her granddaughter's comment.

Derek stretches his arm over Zola and wraps it around Meredith's shoulder. "Zo's gonna ace human anatomy in med school. Aren't you, Zo?"

"He's so handsome. He already looks like both of you," Carolyn says.

"You think so? I think he looks just like Meredith. He got my feet, though."

"And his butt," Meredith adds, mostly to tease him, but also because it was the truth.

A deep shade of crimson floods Derek's cheeks, and he runs a hand through his hair. "Oh, jeez."

"Seriously, identical. I'll send you the pictures," Meredith promises her mother-in-law.

Between Zola's enthusiastic penis talk, and Meredith's unfiltered commentary about his ass, Derek is suddenly more relieved than ever that he's having a son. As it stands now, it's two against one, with favor going to the girls, and he could really use an ally.

...

Zola falls asleep in their bed that night, curled up in Derek's lap after the three of them finished reading the stack of library books about big sisters. She can't get enough of them, soaking in all she can before her brother's big arrival.

"I thought she might have asked for a refund when she found out she wasn't getting a sister, but she's pretty pumped about her baby brother. I think she loves him as much as we do," Derek says quietly, fixing the footie on Zola's giraffe pajamas.

Meredith smiles at her daughter, then looks down at the bump that housed her kicking son. All the logic in the world wasn't enough to explain how and why life had decided to bless them with so much; they were just grateful that it had. "I can't believe how much I love him. Both of them."

"I know." Derek keeps one arm cradled around Zola and puts his other hand next to Meredith's on her belly. "We have kids, Mer. Plural."

"Right? How did that happen?" Meredith asks.

Derek smirks at her with a dirty glint in his eyes. "Well, he's the result of some hot morning S-E-X that I'm very glad we decided to have."

"Yeah. Putting him in there was a lot more fun than pushing him out is going to be," Meredith says, the idea of childbirth becoming more daunting with each day closer to the due date. The nerves spark again, so she reaches for the trusty pack of Peeps from her drawer. "These were supposed to be for Zo's Easter basket. Remind me to buy more for her."

"Okay," Derek chuckles. "And Mer, you're gonna do great. I'll be there the whole time. You can yell at me all you want."

"Thank you," Meredith says as she chews.

Zola lets out a tiny yawn as she stirs, looking up at Derek with hooded eyes. Derek rubs his hand over her back gently. "Hey, Zo. Do you have to go potty?" he asks.

Zola shakes her head. "No. I didn't kiss my brother goodnight." She crawls off Derek's lap and settles herself next to Meredith. "Night-night, Aladdin. Zozo loves you," she says softly.

"He loves you too, Zo," Meredith says.

Zola cuddles herself as close as she can to her in-utero brother, who started thudding his feet when he heard his sister's voice. Zola wraps her small arm around her mom's belly, nuzzling her nose into Meredith's shirt. "I sing you to sleep, okay?"

Her parents listen as she sings him The Isty Bitsy Spider the whole way through, and to Meredith's surprise, the singing actually soothes the baby down. The kicking tapers off as he settles for the night, and by the time Zola makes it to the end, they're both asleep.

Derek is almost afraid to speak and risk disturbing the peace. "Well, now we know she's good backup for when neither of us can get him to sleep at night," he whispers. "It'll give you and I a chance to work on kid number three."

"Yeah, let's see how this one goes," Meredith laughs. "There's a good chance you'll be going to the carnival alone for a while."

Derek grins. "That's okay. Some rides are always worth the wait."

With a smile like hers and a dimple beneath your chin
Finger nails the size of a half grain of rice,
And eyelids closed to be soon opened wide