I like the idea of starting them at about 6. Some fledgling ability to read English (or whatever their native tongue) is helpful, though not necessary. At that age a 1/2 or 3/4 nylon strung guitar is ideal, even if it's outgrown quickly, and it can be handed down or traded up. I will not start a student that age on steel strings or a large body guitar...that's like trying to ride a bike without reaching the peddles.

Parental involvement helps, but sometimes isn't possible. Encouragement is paramount. Little stickers on the lesson sheet are a con, but sometimes it takes a con to get started. A smile and a bit of praise, sincerely, works better than browbeating. A sympathetic teacher can transform a student, the opposite is tragic.

My experience is that I can teach them easily how to read music when they're young. Once they're teens, it's harder, particularly if they prefer rock tablature.

Good luck.

Peace, Mooh.