This is pretty much what I expected - girl and brother end up in a fairy tale world, alter history and help Snow White. The narration is breezy and funny, the time travel aspect makes sense, the kids have realistic reactions to danger and weirdness, and I especially liked how Snow White became a more assertive person. I was not a fan of the line "Who doesn't know what a phone is?...Maybe she's homeschooled." 
 These are popular at my library, and seem to be at about a 2nd - 4th grade level.