From the Sherlock anon-meme, but don't worry--it's completely gen. I don't usually bother with recommendations, but I kind of want to bookmark this for myself whilst sharing it.
Title:
Milk and TeaRating: G
Pairing: some background John/Lestrade, though their relationship isn't the point
Summary: 7 year old Mycroft and his 2 year old brother are orphaned, leaving Mycroft to take care of Sherlock. John and Greg, the couple looking to adopt them, are perturbed by Mycroft's acting like Sherlock's surrogate parent. Keep a tissue box handy--your heart will ache for wee!croft.