I recently moved to Germany to live for a few years so am using the Pimsleur German for myself. One thing I have done is cut the lessons in half (so 60 15-minute lessons for Level 1) because 30 minutes was just too much for me to retain and find time for. But since I cut the lessons in half, I am allowed a bit of time to supplement with a grammar book and vocab app (Babbel for iPhone–it’s great, free, and even my kids are learning vocab with it.) The combination of the three are working great for me, but I am an adult, and a grammar book probably won’t do much for a young child other than make a nice addition to a pretend library (as for my kids). Oh, and I tried a bit of Rosetta Stone but it just annoyed me for some reason.
One interesting thing I noticed about the Pimsleur that some might not like for using with younger kids is that, in the German version at least, I learned to ask for a beer or wine before water. I remember that by lesson six I could invite someone over to my house for a drink but coultn’t ask where the restroom was. But I can’t think of anything else really odd like that in the 24 lessons I have done so far.
So in 24 lessons, I still can’t hold much of a conversation with my non-English speaking landlord, but we try to get by in the few phrases we know of each other’s languages. So I can’t speak for how well Pimsleur teaches one to speak and understand the language when used in it’s entirety, but maybe I will get there! It does seem to be a fairly simple yet effective way to get going in the conversational side of a language.
Not sure if that helped at all since you were asking more about kids. Either way, hope you find what will work the best for you!