Maybe something less "other worlds"? These should all be suited to a 12 years old, though of course it is up to you: Back to the future (1, 2 and 3), Time aft

Maybe something less "other worlds"? These should all be suited to a 12 years old, though of course it is up to you: Back to the future (1, 2 and 3), Time after Time (1979), Gattaca