The Kid (movie, 1999)

Powerful businessman Russ Duritz is self-absorbed and immersed in his work. But by the magic of the moon, he meets Rusty, a chubby, charming 8-year-old version of himself who can't believe he could turn out so badly -- with no life and no dog. With Rusty's help, Russ is able to reconcile the person he used to dream of being with the man he's actually become.