Warmly referred to as "The Flight of the Alligator" within our family, this classic 80s film saw a little kid take control of a space-ship and travel through time. His family think he's gone missing, but when he walks back into their lives 20 years later (but without ageing) their entire world is turned upside down and the kid is studied by various scientists.
Eventually, scared of the future, the boy (I keep thinking he's called Elliot but that's the boy from E.T.) tries to make it back to his own time and place.
He does in the end, of course. How predictable.