A Study in Honey
I alwys worry when I write these things that I will sound like John Watson, because "fantastic!" and "amazing!" are the first words that come to mind. Or that I'll end up paying a backhanded complement to the fandom by saying something along the lines of "You know, you don't often see fics that do ____ well, but here's the exception." I can't think of another way to describe this one-shot than amazing, though, precisely because you don't often see fics that both show a heartbroken Sherlock in the wake of John's absence without it being a trudging angst-fest, and you also don't often see parentlock stories that operate as more than just "genre" fic. Not that there's anything wrong with genre-fiction, but this story feels like a convincingly canon Sherlock interacting with a child, rather than a story about parenting or children per se. And it's, well, fantastic.
If you liked the Archie character and would like to see more of him, I highly recommend this story. Ditto if you like a paternal Lestrade looking out for Sherlock, or a prickly-but-still-human consulting detective. I know the author from Tumblr, which is probably why I read it (there's so much fanfic to read out there, I'm sure I'm missing out on all kinds of jewels). But that's not why I'm recommending it so heartily. It's genuinely a very worthwhile quick read that did a very solid job on characterization and was just plain fun.