My 9 year old son wants to play bass guitar and my 6 year old son wants to play (regular) guitar. Do any of you who have teaching experience think the 9 y.o. should start with: 1)full size or 3/4 or 5/8 scale instrument? 2)4 or 5 string? 3)full or small size guitar for the 6 y.o.? They both want full size instruments and one could argue they won't have to make an adjustement with their hands and technique in few years. However, their hands are significantly smaller and barre chords and runs on the low E or B string on the first four frets will be difficult for them.