I have a prompt, if you’re up to it. I know you write the boys around the age of two, but what if John regressed even smaller one day, like a /baby/ baby, and Sherlock got to be the big brother for a day? Just a random idea should you want to do it.

Sadie: I’ve been getting so many good prompts lately! These are gold, guys!

“My’coff?”

“Yes, Sherlock?”

Sherlock looked up at his big brother from the floor. “Why, um, why is Jawn…” He looked back down at the extremely regressed man laying on a pile of blankets next to him, chewing an infant’s squishy, fabric block, then turned back to Mycroft. “Why is Jawn so, um, so qui’id?”

Mycroft pushed his chair back from his desk, stood up, and came over to them. He stooped over Jawn, gazing down at him, then reached and gently took the block from his hands and gave it a small shake in front of the little doctor’s nose, making it jingle. “Because he’s a very tiny little baby today, isn’t he?” he said with a fond smile playing on his lips.

Jawn responded with a big, toothy grin and a happy gurgle.

Sherlock watched, fascinated. Jawn was never this tiny. Never tinier than him. “A y’ittle baby?” he asked, crawling closer.

“Gentle,”Mycroft reminded him, and then handed Sherlock the jingly block. “Can you be a good big brother and play with him while I warm a bottle?”

Sherlock’s head snapped up, his mouth open in a ‘O’ of surprise. “Big br’ovver?” he asked, his voice soft with mild awe. He’d never been a big brother before.

“Yes, a big brother.” Mycroft stood up and ruffle the front of Sherlock’s hair. “Would you like to give him his bottle when I return?”

Sherlock’s eyes widened, and he beamed up at his brother. “Y’ah, p’ease!!” he babbled, returning his attention back to Jawn. “I do i’d!!”

“Then play nicely…I’ll be in the kitchen if he begins to cry.” Mycroft  made his way out of the room, but stopped just on the other side of the doorway, out of sight, and peered back in…

Sherlock had picked up a different soft block from the pile nearby, and was squeezing it to make it squeak in Jawns’ face right before pulling it away as the little doctor reached for it, kicking his feet and giggling.

Mycroft waited until Jawn finally caught on to the game and succeeded in grabbing Sherlock by the wrist with a clumsy hand, making Sherlock cheer “Yay, Jawn di’ i’d! You di’ i’d!”, before he turned away to go make the tiny doctor a bottle.

Mycroft smirked; of course Sherlock would be a good big brother. He had, after all, learned from the best.