Great job so far. This is one of the better time-travel stories that I have come across, probably because it is taken from the perspective of a believable OC.
A point to watch out for though is to not make the kids too magically adept before reaching Hogwarts. Canon strongly suggests that (even for pure bloods) magic doesn't become reliably stable for kids until they are about eight or nine years of age.
Learning the theory beforehand is easily believable, but having a first-year possessing a fifth-year's practical ability isn't. (even if it is Mr Exception we are talking about)
Two questions, though:
Did you realise that Rose's address is an actual real-life address that can be spotted on Google-Maps street view? (house number and all)
Why do I get the feeling that Rose is actually Harry's daughter rather than Ron's? (Ron's behaviour around her, her relationship with Harry, the blood wards actually working at her residence...)