Factual error: In the scene where Bobby and Mike go into the comic book store, you can clearly see a Transformers comic on the shelf. But the movie is set in the late 1960's/early 1970's....and Transformers did not come out until the 1980's.
Factual error: The walkie-talkies the kids use at the end of the film would not make the squealing noise they do. The walkie-talkies they have transmit on high enough frequencies that this would not happen. Mediumwave and Shortwave have this effect, not walkie-talkies.
Answer: He was in a very small part of the movie and at the time he had already become quite a famous star. If his name were attatched to it without being uncredited, he would have had top billing. He probably decided to remove his name from the movie so the younger actors could receive more attention. The same type of thing happens in quite a few movies I can think of.
jennibee