You are right. There are 2 products: "RPG Maker" and "Game Maker". My son too uses Game Maker . The best description is on the Web site:
Using easy to learn drag-and-drop actions, you can create professional looking games within very little time. You can make games with backgrounds, animated graphics, music and sound effects, and even 3D games! And when you've become more experienced, there is a built-in programming language, which gives you the full flexibility of creating games with Game Maker. What is best, is the fact that Game Maker can be used free of charge.
In fact, the programming language is Game Maker script (GMK) and it's a very good graphical learning language.

My eleven years old son's love programming game with RPG Game Maker. It's a programming language build in .NET. It's allow kids to program RPG game using pre-defined objects. Since he programs with Game Maker, my son knows how variables, events, loops, objects, bitmaps, sounds, etc works. I recommend it to everyone!