Fred Savage is not 4 in this movie
No way.
That has to be an error.
I was just watching this movie earlier today with my niece because I remember really liking it when I was her age and yes it's my mom's old VHS copy. Anyway, I did notice that there were two copyright dates on the box and in the end credits. One is for 1980 and the other 1987, now obviously Fred Savage is not four years old in this movie so it can't be 1980...or can it? I think it's both actually so hear or read me out here.
My theory is that the movie with claymation stuff that isn't narrated by Fred Savage but is narrated by his character was done in 1980. Then for some reason they decided that they could add something to the movie by putting in a popular child actor. So basically the first part of the movie with Fred Savage is shot in 1987 then put with the original movie done in 1980. To me, it makes sense but maybe I'm over thinking this.
The original 1980 short is contained within the context of the 1987 video, complete with the original credits at the end. It lists someone named Michele Mariana for the voices. In the original short, Philip's voice sounds like an adult woman doing a kid voice (kind of like how Nancy Cartwright voices Bart Simpson), and the voices weren't changed when it was included in the 1987 video.
So Fred Savage wasn't involved in the original short, it was Michele Mariana doing all the voices, including Philip.