WHAT MOVIE IS THISSSS?

Ok so it starts out where this kid is taking his dog for a walk, and he falls down a hill (maybe into a river). He gets up and goes home and there is a different family living there. He realizes hes in the future, but hes still the same. He tries finding his young brother who is now older than him. Also i remember he travels around on this silver spaceship with an alien. HELP! Whats the name of that movie!