Woah, woah, I don't vouch for it for adult education. Adults learn language differently than do children (which, of course, you already know). Adults are able to learn the logical rules of grammar and use intelligence apprehend the language. Rosetta Stone is not very grammar focused, but I'm sure it provides a solid beginner's vocabulary; I could also see it being useful for an adult who can't stand grammar, can't attend classes, or wants to get some basics under his or her belt. As with any self-study system, it is, at best, an incomplete system.
Edit: Duh, just realized you were talking about Pimsleur as being the one I vouched for.
Pimsleur is what it is... it teaches you basic conjugation and how to engage in simple conversations in the language. It would probably be boring for a child who isn't highly motivated.