I have read something similar to this a long time ago, about a year, so if you recognize it, PLEASE let me know and i will give you idea credit and what not.
This is amazing and set about 1 year after Season 3, so there are sort of spoilers (?) but if you haven't seen season 3 yet, i don't know how you're reading fic omg GO WATCH IT
This gets a little steamy, but not smut.
Sherlock and Molly often found themselves looking after Hannah Watson. Now at 7 months old, she was a lot harder to handle and often got herself into a sticky mess. In this case, an ice creamy mess. And seeing Molly in a similar situation, has left him feeling rather uncomfortable having the baby in the room.
"Hannah sweetie stop it!" Molly said with a laugh as she was trying to her throwing the ice cream all over the flat. And then took the little ones ice cream and put it in her own mouth before taking her out of her high chair and resting her on her hip. Hannah, still sticky and wiggling began to laugh, at Uncle Sherlock for pulling faces. Molly was far from amused.
"For someone that doesn't like children, you don't half like Hannah," Molly shot at him, after taking the ice cream out of her mouth.
"Molly, we've been through this. Hannah's smart and cute and it's not that i don't like child i just-"
"Don't like mess or sticky or ice cream. Yes i know, so can you please help me?" and Molly handed a giggling but sleepy and very stick Hannah to Sherlock and put the ice cream back in her mouth and began to tidy up. Sherlock sat with Hannah while watching a Molly wipe down the high chair and eventually Hannah and that's when Sherlock began to cap his thoughts as inappropriate.
Molly was bent over in front of Sherlock, given she was tending to a sticky baby on his knee but she was there all the same. Covered in ice cream and a little flushed and the ice cream in her mouth making her dribble a little.. Oh god, this was a problem.
"Molly take the baby."
"Wh-" Molly began, with difficulty having still got the ice cream in her mouth.
"Molly I think it's best if you take Hannah."
"Sh-"
"Hello," Mary called up the stairs. "Where's my little monster?"
Sherlock rose, practically throwing the baby at Mary before Molly could even speak.
"Mary. It's been fun. Hannah's been great. Any time, blah blah. I really need you to leave now."
"Sherlock!" Molly shouted. "Don't be rude, I wanted to-"
"Sweet, it's ok. John's in the car anyway, we can't stay. I'll talk-" and Sherlock slammed the door.
"What was that about?!" Molly asked. "I wanted to talk to Mary about-"
"Molly," his voice was dark and strong and she was already blushing, he only said her name… He turned, looking at her and took two big strides to reach her, hovering over her, making her feel weak at the knees. "I don't think i told you the entire truth before." He broke off reaching down and sliding his hands down her waist and cupping her bum. His lips passed over hers and then down to her neck, licking and sucking gently at the sticky.. "Molly. I. Really. Fucking. Love. Ice cream." And his lips found hers. Molly let about a muffled moan and Sherlock picked her up and carried her to his bedroom. But not without stopping to pick up the ice cream from the kitchen.