Mr. Walsh from Beverly Hills, 90201 gives Josh his first paycheck.
The Other Marty: Invoked during filming. Reportedly, Penny Marshall had David Moscow perform scenes of the grown-up Josh to help Tom Hanks get a handle on a how a kid would behave in an adult setting.
Throw It In: The "Big rap" sung by Josh and Billy is one Tom Hanks' son had learned while at summer camp.
Tom Hanks Syndrome: This movie marks Tom Hanks' transition from a comedic actor to a dramatic actor, even though the movie was part comedy, part drama.
What Could Have Been: Robert De Niro and Harrison Ford were considered to star as Josh when he becomes an adult. Sean Penn was also considered for the role. Also, Debra Winger was offered the role of Susan, but she turned it down because she was pregnant at the time. She even recommended Elizabeth Perkins for the part.
Steven Spielberg considered directing the film (his sister co-wrote it, after all) but declined as his son had been born and felt he should be closer to him. Ron Howard and Sidney Pollack also turned down the directorial job.
The film was originally supposed to end with Josh back in school and meeting a girl named Susan — who turns out to be the same Susan Josh met in his time as an adult, and made a wish on the Zoltar machine to become a kid again. This was rejected by test audiences and replaced with the ending where Susan watches as Josh turns back into a kid and walks out of her life.