I too learned to play the drums and saxophone before trying to play guitar. The only real reason that i would say to learn to play acoustic first is that you build more hand strength, which makes the transition to electric much more exciting because you are allowed to do stuff that you couldn't do on an acoustic; however, with your child's age, hand strength might be a problem in general so electric might be the way to go. A friend of mine's younger brother started at about that age and he probably had an easier time with it because he can do a lot with just power chords. Back to learning the drums first: It is much more exciting to learn the drums first, plus your rhythm is developed much better. My roommate and I both play guitar, with guitar being his first instrument, and it being my 3rd. Since i have such a stronger sense of rhythm, i feel that my guitar playing is much stronger, even if he has more actual coordination with the instrument. In my opinion, it's not how far your fingers can spread or how fast you can move them that make you a great guitar player. Like all instruments, it transcends actual coordination into feel and understanding for rhythm and melodies. It might make it easier for your child, but it is not a necessity. The most important thing is to keep practicing.