The movie was about a boy who accidentally travels back in time. He ends up on a field during a war. He also meets a girl about the same age; I think they were 10-12 years old.
I forget the middle of the movie, but I remember that at the end he went back to his own timeline and searched for her.
He found her and she was very old because time had passed for her, but he was still young because of time travel.