[reikonomusha]

To be clear though, a lot of kids do understand the current notation system fine. Most kids aren't saying "hey! this chord is a minor third in frequency space but occupies the same vertical distance on the page as a major third! so confusing!" They instead approach it very much "monkey see, monkey do".

That's not to say many folks don't have trouble with notation, but if I had to place a bet, almost any notational system that abstracts away from letter names or (in the case of piano) keyboard positions will pose difficulties.