Sadie:

“Molly.”
Little Molly didn’t answer straightaway…all of her concentration was focused on getting the super-special-shiny-dino stickers that Sher’yock had given her to sit on the Lego block juuuuuuuussss’ ri’de before pressing down and sticking it into place.
Because, as Molly knew, once you stick a sticker, it’s there FOREVER. So you have to be totally, completely, absolutely 100% sure that you stick your stickers somewhere safe.
Because it’s stuck there. FOREVER.
“Molly,” John tried again.
Molly hunched down further over the lego in her hand, the tip of her tongue poking out in concentration.
“Molly. MOLLY. MOLL-EE. MOLL-EE HOOP-AH!”
Molly finally got the tiny, three-horn-shaped sticker centered and pressed it down, cementing it forever onto the tiny plastic block with a delighted “Yay!” and a happy bum wiggle.
John threw up his hands and gave Sherlock a look that perfectly encapsulated an emoji that the detective had seen used more than once in text messages from the good doctor himself: “ D:< ”
Sherlock was pinching his lips and nearly asphyxiating on his own, barely contained laughter. He shook his head and looked away while he collected himself (in order to not get murdered in front of the sweet little angel-tot under their care today), and when he finally felt back under his own control, he looked down at the little pigtailed munchkin sitting at his feet. “Molly,” he said, nudging her bum with his foot.
Molly looked up from the sheet of stickers in her hand. “Wha’d???”
“Uncle John wants your attention, darling.”
“Unc’a Jawn?”
“Yes…he’s been trying for several minutes.”
“Ohhhhh…why didn’, um, why didn’ he say so???”
“I did.”
Molly whirled around and looked up at John, her eyes widening. “Oh….Hiiiiiiii, Unc’a Jawn!” she chirped, genuinely surprised to see him there.
John’s face visibly softened, and Sherlock smirked; John was such a pushover, and didn’t even know it.
John bent down with his hands on his knees; “Molly, sweetheart, precious, cupcake, baby doll, angel…where did you put my phone?”
“Your wha’d???”
John’s smile never faltered, but it lost a bit of the, uh, the shine. “My phone, darling. You know, I let you play a game on it?”
Molly gasped; “Ohhhhhh, Can’ee Crunch???” she asked, clasping her hands under her chin. “I y’uuuuuuuub tha’d game! I bea’d i’d an’ go’d a high score, a’–!”
“That’s wonderful princes, but where did you put it when you were done?”
“Where I pu’d i’d?”“
John’s face looked as if it were close to cracking. “Yes, darling,” he said slowly. “I need it back; where did you leave it.”
Molly tilted her head and bit her lip while she thought. “Ummmmm,” she hummed out loud, then wrinkled her nose and shrugged. “I dun’no!”
John’s smile seemed to be unnaturally frozen in place. “…What.”
Molly shrugged again, and giggled.
“John.”
“Molly, I need you to find my phone. Now.”
“John…”
“Shut up. Molly, Uncle John isn’t kidding around, one…”
“John.”
“If I have to get to three, you’re going on the naughty step. Two…”
Just as John was opening his mouth for a ‘Three’, the back right pocket of his trousers started to vibrate, causing his mouth to snap shut just as his ringtone started to play: “Ooga chaka Ooga chaka Ooga Ooga Ooga chaka…”
Sherlock and Molly both burst out laughing as John reached into his back pocket and retrieved his phone, only to see that it was Sherlock himself calling. “What the hell–???”
Sherlock wiped his eyes while Molly was still doubled over, clutching her belly. “G-good girl,” he stammered, and held his hand down for a tiny high-five. “Very, v-very good!”
John just stared at them as if they’d lost their minds…and at this rate, they may very well have. “What.”
Sherlock cleared his throat, thought his was still grinning like…well, like an idiot. “I, I bet her a new outfit if she could find a way to get your phone back onto your person without you noticing,” he explained, still chuckling to himself, and then reached down for Molly. “And she did!” he cheered, lifting her into his lap. “Clever girl!”
“Ha-ha-ha,” John said flatly. “Yes, I’m the idiot, now both of you can go sit on the step, ha-ha-ha.”
Molly giggled and leaned back against Sherlock’s chest while he gave her a peck on the cheek…
“Wor’f i’d!”