Well I can contribute this to the Topic. There was this language learning children's cartoon series called Muzzy (You can find it on YouTube if you want now). Well anyway I watched the German version with my younger brother and what I can say about it is this, It will not make you child fluent in the language, however, to this day I can still count to 10 in German and say Good morning and goodnight. My theory is that because I was younger, my mind was more elastic and more open to learning new things so everything I learnt from the show was stored in my mind, even if I didn't learn very much.