My DS is 3 and loves both of those movies. Of course, his favorite movie is Star Wars and the Harry Potter movies
He's weird when it comes to cartoony type movies. they scare him way more than noncartoony ones do. Example: he refuses to watch most of the Disney movies because they are "too scary and have bad guys" but he will watch the whole Harry potter movie and not even blink.
I think as long as you talk about how that stuff is not real there should not be a problem. They are made for kids to watch.