The first time it happens, Sakumo is a newborn and determined to let the world know how very much he disagrees with the horrible act of being born.

Kakashi would, in fact, love to voice his own complaints about being saddled with a - very loud - baby he hadn't planned for or intended, he'd have really liked to have complained about how the mother opted not to help and, as he was the higher ranked of them, it became his responsibility to care for their his the child. He didn't and it was not in no small thanks to his sensei, who did not care for complaints, and Orochimaru, who would have just told him that it was his fault and if he wasn't prepared to face the consequences of his actions then he should have restrained himself.

He wanted to, though, he very much wanted to.

Sensei had told him, briskly, when she had visited to see his son the child for the first time and found the baby wailing for all the world to hear, that it wasn't uncommon for babies to cry after being born or even for a few days afterwards. "They're used to being surrounded by their mother's chakra," she told him, "So coming into the world and fining that their mother won't - can't - envelope them in their chakra as in the womb is a shock - an unpleasant one at that."

Which, well, Kakashi had an answer but he had wanted a solution.

"If you're used to being surrounded by chakra-..." he broke off, blinking when the wailing stopped and he turned to find the baby looking at him from where he had put it. There was a beat of silence before the baby resumed it's screeching and Kakashi hurriedly went on talking, "Then would it help if I cover you in my chakra? Or no, since I'm not your mother?"

The baby hiccupped, fisted hand rubbing at it's face.

"I'm going to try something," he told it, approaching cautiously. "There's no reason to scream, I'm just going to pick you up-" He promptly did so and was startled when the baby latched on to him. "And I'm going to just-"

He didn't finish, instead he focused on manipulating his chakra to cover - but not smother - the baby in his hold. It started to whimper, face scrunching to cry but, before he could pull his chakra away, it's face relaxed and the whimper changed into a coo. He wasted an hour like that, holding the baby with his chakra around it and just talking - he eventually, in desperation, started reciting various mission reports from memory - to it until it started to drift off and he deemed it safe enough to put it back to bed.

He was wrong, as soon as he put his son the child down, it started wailing again and he had to spend another half-hour to get it to drift once more. It was two more tries - once where he'd actually managed to leave the room before it started screaming - before Kakashi got that the baby wouldn't allow him to put it down, even to sleep.

Kakashi took it to bed with him, laying on his back and letting it nestle into his side as he used his arm as a barrier to keep it from rolling. He barely slept, too worried that he'd get caught in a nightmare and injure the fragile thing thus earning a scolding from his sensei, and was wide-awake as morning came with dawn light filtering through the apartment window, highlighting the child's hair that was so similar to his own.

"Oh," Kakashi said, reaching with his free arm to gently brush his knuckles against the soft baby-flesh, as it hit him like a revolution, this is my son.