My daughter is 11 and she, along w/ all her friends, enjoy trying new hairstyles. You could expand the braids and extensions to updo's and other fun ways of wearing pony tails, pig tails, etc. You could also expand to how to wear light make-up (w/o looking trashy), how to do a proper manicure/pedicure, basic skin care. This is a great niche market for you. Wasn't clear if you're planning to create a brick and mortar store or some type of online teaching site.

Good luck!