in the book Annabeth and Percy are 12, but in the movie they are in their teens.
in the book Annabeth has curly blonde hair and in the movie it's straight and dark.
in the book Clarisse was the camp bully but she doesn't appear in the movie
The Hydra does not make an appearance in the book but it does in the movie
Ares has a main role in the book but only appears once in the movie
here are just a few