Pick up activities brochures for Cary, Apex, HS and Morrisville at the Libraries/Community centers. The Cary one is huge and offers the full range of art classes - drama camps - sports - nature classes.
You will not believe the (reasonably priced) options out there just offered by the various Towns for kids that age.
We have enrolled in a half dozen sports through the various town programs, and other classes through the local YMCAs (gymnastics/swimming) and centers like Dreamsports (Apex) and Netsports (Cary).
Your biggest problem is going to be narrowing down what to do!
Your son will love it here. Playgrounds, bounce houses and kid's museums galore.
Does he start K this Fall?