Answer:
In the book and in the movie, he yells out, "Moonchild," but I seriously doubt that Moonchild was actually his mother's name.
According to the Related Question (see below) his mother's name is Sarah. But I'm not sure if that's correct or not, since I do not remember his mother's name being mentioned in the film. And I've seen that movie dozens of times since I was 4 years old.