Buckwallow is great mix of easy flow trails for your 6 year old, and excellent technical rock riding that is unlike anywhere else in the province. Trails are beautifully maintained, and accessed from a fire-road loop (so you can easily omit the hard trails for your son without impacting flow).
The difficulty ratings are posted for each trail from 1-5. Anything 3 or less should be fine for your son, with a few walkarounds. Try the 4’s if you’re feeling brave, don’t bother with the 5’s unless the 4’s seem too easy (The 5’s are a real challenge, and unridable even for most experienced riders).
You have to pay cash, its about $10. Ride from 1-3 hours depending on how many trails you add.