A long time ago I remember a movie about a boy having some sort or disease or maybe cancer and he was sitting in a tree house when a man came up to talk to him while a lady staying on the ground to wait. Also, there was a teenage girl and guy talking outside of a restaurant and the guy walks out into the street and gets hit by a car. I don't know if he died but I remember that the girl witnessed this happening.

Any help would be appreciated. Thanks

Its not 'Simon Birch' or 'The Mighty' is it?

Sadly no.