Oh, so many things... Allow me to begin.
In the book, Winnie is 11. Not a teenager. So she shouldn't be kissing Jesse at all. Yes, it does make it a little creepy when Jesse's like "hey winnie wait six years then we can get married" but from his standpoint of immortality, six years is nothing.
There's also the whole thing in the book (and musical) where Winnie dumps the water on the toad, making it live forever. In the movie, SHE RUNS HER HANDS THROUGH THE WATER! IF SHE DID THAT AND DUMPING IT ON THE TOAD MAKES IT IMMORTAL, SHE SHOULD BE IMMORTAL!
But of course the movie removed the ENTIRE toad thing, just occasionally showing a random toad. At the end of the book, ALL of the Tucks (not just Jesse) visit Winnie's grave, then as they're driving away, the toad is in front of their car and only moves at the last second and Angus Tuck (the dad) says, "Dumb toad thinks it's gonna live forever."
In the movie they removed the importance of the toad!!! That toad was the best part of the book!
Thank you for coming to my Ted Talk.