A friend who plays recorded music and sings constantly finds that her three year old and five year old have fantastic memories for songs, and also have impeccable pitch. Picture her embarassment when the three year old started singing "Three Drunken Maidens" and "Plastic Jesus" in church!

That doesn't answer your question, but I think that lots of exposure outside 'the classroom' is probably as important as the formal learning time.

A more concrete (?) suggestion: when I learned guitar around 8 years of age, the chords were simplified for us, so that "C" was just one finger on the first fret of the "B" string, and so on. For ages we played songs (folky stuff - Red River Valley, Home On the Range etc) with only C, F and G7 (that last chord was one finger only on the first fret of the "E" string). I soon cottoned on to the idea that when a melody goes a certain way, the chord will change but then probably finish on a C.

Hope that's not too basic - I had fun reminiscing, anyway!

Callie