This fic is a lot of fun and you really sucked me into the story early on. I got a huge giggle out of Snape thinking Harry was too oblivious to notice certain things (the quality of his robes, for example), and then Harry spotting them without effort. I definitely appreciate that your Harry isn't an idiot. And in denial!Snape was perfect. :P
Normally I wouldn't buy a Snape who's good with kids, but it works here -- because Snape takes this job out of sheer desperation, and then somehow finds himself with a family before he's had a chance to realize what hit him.
Great job with all the Quidditch details. And the medical ones. The tension in this story was fabulous, and the entire thing was paced wonderfully. Nice!