A/N: This one-shot came entirely off the top of my head. It was inspired by an Instagram post I saw and some of the ideas in this will be derived from it. I believe it was posted on tumblr by incorrectbbcsherlockquotes. So I hope you like it and don't forget to favorite and review!

Mycroft Holmes

Mycroft Holmes had been holed up in his office when the text came. He had been going about his business. A pleasant day it was, he worked out quite a bit at sunrise and even helped himself to a piece of cake afterwards. Frankly, Mycroft was enjoying his day until his phone beeped.

Baker Street.

NOW

Mycroft was in motion in a instant, his assistant had his car readied almost immediately and he was on his way. He made calls to his people in the area to monitor whatever the situation was at his brother's flat, he even made a call to Lestrade.

Mycroft subconsciously played with the handle of his umbrella. Mycroft was always worried about Sherlock, and that only intensified after the episode with Eurus. Mycroft himself had been incredibly shaken after that, though he would never admit it out loud. Things had been relatively quiet since. Mycroft was condescending and hard on Sherlock, but he was simply like that. He cared for few; his parents and siblings, even Eurus despite what she had become but Mycroft had a particular soft spot for Sherlock, and perhaps only for him. Magnussen had not been wrong, his little brother was his weakness.

Mycroft was out the door the moment the car pulled over in front of 221B Baker Street. He entered and climbed the stairs as quickly as he could, barging into the room to find Sherlock and John seated in their customary seats. Mycroft noted that John's two and half year old toddler was on her father's knee.

"Ah, Mycroft. I was wondering why you were taking so long." Sherlock greeted amicably.

"What happened?" Mycroft panted.

Sherlock got up and grabbed his coat, "Nothing in particular. Lestrade has a case for me and John." He turned to Mycroft with a sweet smile, "Be a dear, brother and look after Rosie while we're gone."

Mycroft starred at Sherlock, "You must be joking."

"Of course I'm not. Mrs. Hudsen is out of town to meet a friend and Molly is down with a cold."

"You called me here to babysit?" Mycroft demanded through clenched teeth. He noticed John wearing an infuriating smile on his face, clearly enjoying Mycroft's predicament.

"Yes, brother mine. Come on, John." Sherlock smiled innocently at Mycroft before exiting the room. Mycroft wasn't even given a moment to protest.

The next thing Mycroft knew John was handing over the small toddler to him.

"Everything you need to know is in that binder." John pointed to a binder on Sherlock's desk, " I had already made it for Sherlock. Being a man as brilliant as he is, he sure doesn't know anything about babies."

"Neither do I."

John chuckled, "That's what the binder is for, Mycroft. Call if things go entirely out of hand." John grinned at him and patted him reassuringly on the back and was out the door.

Mycroft starred blankly at John's retreating back. He snapped out of his shocked state when the child in his arms started babbling. He observed the baby, she had inherited her late mother's hair but wore it longer, Mycroft saw many of Watson's features as well. The baby was in turn studying Mycroft, eyebrows scrunched up in concentration. He doubted that any intelligent thoughts went through the child's small brain. He doubted if any would go through her head when she grew up if she took after her father.

Whatever John's baby saw in Mycroft she seemed to like it. She smiled at Mycroft causing his eyes narrowed at her, this just made her laugh and babbled happily. Mycroft studied her for a few moments later and with a exasperated sigh walked over to binder. He grabbed it, took a seat on Sherlock's couch and began to read. The child seemed to get increasingly restless so Mycroft let her down. He watched as she waddled around, smiling at him every now and then. But the toddler was still impatient as she was unoccupied. Mycroft scoured through the pages for instructions on what to do in such a situation.

Drawing. Just give Rosie crayons and paper. (In the drawer.)

Mycroft retrieved the items and handed them over to the baby. She cheerfully accepted them and sat herself on the floor and started taking out the crayons out of the box. Mycroft pursed his lips in disdain at the disarray caused but refrained from saying anything, after all she was just a child. Mycroft retook his seat and started texting, once in a while he would glance at the child on the carpet. Everytime the little human caught Mycroft watching her, a smile would form on her face and he would quickly avert his eyes.

"Uncle Mycroft." A small voice called after a fair amount of time. Mycroft looked up to find the child grinning at him and raised an eyebrow, 'Uncle Mycroft', they weren't even related, Mycroft suspected Sherlock's influence when it came to that.

"Yes?" Mycroft drawled disinterestedly.

Watson's child held up her drawing that she had worked on for so long. The paper was filled with scribbles of various colors but amongst the scrawls, Mycroft spied two stick people holding hands, one taller than the other, who wore what appeared to be a suit. The other had long yellow hair.

Mycroft's gaze returned to the toddler who looked extremely pleased with herself.

"Uncle Mycroft." She pointed to the tall figure in her drawing and then towards to blonde, "Rosie."

Mycroft starred at her, the child gazed expectantly at him. Mycroft peered at the portrait again and felt something warm in his chest at the sight of it. A feeling Mycroft did not experience often, he cleared his throat nervously,

"An exquisite piece of art... Rosie." Mycroft commented with a small but surprisingly genuine smile. He suspected Rosie did not understand what he had just said but she was content with it and went back to decorating the edges with her crayons.

Soon Rosie grew bored of drawing, waddled towards Mycroft and tried to climb into his lap. Mycroft watched in fascination. Being unsuccessful in her attempt, Rosie contented herself with hugging his legs. Mycroft tried to pry her away from them, but she just laughed and hugged tighter in response.

"I have things to attend to, baby. Get off my leg." Mycroft ordered.

Rosie shook her head and clutched his leg even tighter, threw her head back and laughed.

"Let go." Mycroft repeated but this time with a little steel in his voice. Rosie detected Mycroft's change in tone and noticed Mycroft's stern expression. Her laugh slowly died, she let go of his leg and plopped herself beside it. She starred at Mycroft's face with big eyes and tears started to forming in them. Mycroft regretted his behavior and frantically tried to calm Rosie down.

"Please don't cry, Rosie."

Which made her cry louder. Mycroft let out a deep breath and got out of his seat and crouched beside the baby and awkwardly patted her on the head. The crying did not cease and tears were flowing down Rosie's face.

"I was only playing with you, child." Mycroft lied.

Rosie's eyes perked up when she heard 'play' being mentioned, the crying effectively stopped and Mycroft let out a sigh in relief. Rosie grabbed one of Mycroft's fingers, "Uncle Mycroft, play with me?"

Mycroft nodded and Rosie smiled, "Uncle Mycroft, play with me." Rosie tugged his finger.

Mycroft raised his eyebrows, "Uncle Mycroft does not play silly games."

Rosie pouted, "Yes, he does."

"No, he doesn't."

"Yes, he does."

"No. He doesn't."

Rosie sniffled, tears again forming, "Yes, he does." She said through her renewed sobs.

"Fine. Yes, he does." Mycroft gave in.

Rosie's crying immediately stopped and Mycroft's eyes slightly narrowed, he suspected that the little child was manipulating him. Rosie reverted back to her cheerful self, letting go of Mycroft's finger.

"Tea party." Rosie cheered, and waddled to the corner of the room and took out a toy tea set from a bin. She brought them back and motioned Mycroft to sit on the carpet across from her. Mycroft huffed in exasperation but complied.

The next thing Mycroft knew he was sipping from a toy pink teacup, occasionally even fighting a smile as Rosie babbled on in the most sophisticated way she could possibly manage. But alas, a child's attention span lasts for only so long and then little Rosamund was demanding that they play princess, Mycroft was given no other choice but to agree. Rosie played with his hair, put a tiara on his head and drew on his face, all while Mycroft controlled his tongue and huffed in frustration. At the end when Mycroft was shown his reflection, he was appalled.

"Uncle Mycroft beautiful." Rosie clapped her hands in glee. Mycroft annoyance faded and felt the warm feeling in his chest again in its place,

"You really think so?"

Rosie nodded happily. Rosie wanted to continue to play, her next idea was hide or seek. Mycroft actually enjoyed that game a bit, Rosie was really good at hiding and posed a challenge to Mycroft to find her. When he finally did, she burst into a fit of giggles that Mycroft found quite endearing.

After a string of games, Rosie started to tire. Mycroft warmed up some food for her and let her have her supper. He found cake in the fridge and he and Rosie both helped themselves to a piece of it. It was growing dark so Mycroft readied Rosie for bed. He changed her diaper, distasteful business but he knew how to do it. He changed her clothes as the ones she was wearing were a bit of a mess. Mycroft held her until her eyes started to close and took her to the bed in Dr. Watson's old room, placed her carefully on it and slowly made his way out.

"Uncle Mycroft." A small drowsy voice called.

Mycroft turned around to find Rosie sitting up with her hands raised in request. He sighed but went and picked up her nonetheless. She fell asleep almost immediately, Mycroft did not have the heart to risk waking her up by placing her on the bed again and continued to cradle her.

Sherlock Holmes

Sherlock climbed the stairs to his flat, the case had been fairly interesting but didn't pose much of a challenge to him. The answer to the mystery was obvious but Sherlock always did like adding a bit of theatrics here and there. He opened the door to his flat and stopped dead in his tracks at what he saw, he felt John who had been following him close behind do the same.

"Bloody hell." John muttered.

"Bloody hell indeed."

The flat was a mess, well, more of a mess than usual. Crayons, paper, Rosie's tea set and other toys were strewn everywhere. Sherlock spied a drawing on his desk with two people on it, he deduced that they must be Mycroft and little Rosie. Amidst the colorful mess, in Sherlock's chair, Mycroft was napping with his mouth slightly open. There were drawings on his face, and in hair he had a princess's tiara and an assortment of other hair clips. Cradled in his chest was little Rosie, sleeping soundly. Sherlock found the scene quite heartwarming but no less shocking. When he had left Mycroft to babysit Rosie, he had not expected this.

Mycroft slowly stirred and opened his eyes to find Sherlock and John starring at him with their mouths agape. He quickly registered his surroundings and Sherlock could've sworn that Mycroft blushed. He quickly got up, though careful not to wake Rosie. He cleared his throat,

"So how did the case go, Sherlock?"

Sherlock smirked at Mycroft, "Spectacularly."

Mycroft's eyes narrowed at him for moment before he handed Rosie to John. Sherlock noticed a softness in Mycroft's eyes when he looked at Rosie.

"Well I best be on my way. I have important matters to attend to."

"Yes, best be." Sherlock turned around to place his coat on the hanger, but saw through the corner of his eye Mycroft discreetly taking the drawing on his desk, folding it and placing it in his pocket.

Mycroft grabbed his umbrella, "Good evening. Dr. Watson. Little brother." and immediately exited the room with a smile.

The moment Mycroft was out the door, Sherlock grinned at John, "I think we've found a new babysitter." He patted Rosie's little head affectionately.

Perhaps Mycroft Holmes wasn't so cold hearted after all.