What a great story! I love your Snape and Harry, but I especially loved your Ron. Somehow, he just really worked for me.
Erm, though, this is probably just me being dense... I'm not sure I understood how the mystery part of the story resolved itself. Why did someone want to turn Harry into a 5 year old the first time? How did she (Emily) do it? Not sure if it was meant to be left kinda unresolved or I just need to read more carefully / again....
Oh, and I LOVED Hermione's mental processes when Ron and Harry talk-- classic.