The main section of the BGT is section A, there are 2 other sections called B and C. I have done the B section and it is a shorter and less strenous section than the main section. It is still fun and involves some clambering. It takes about an hour and 15 mins for an adult with dogs
I would take a 5 or 6 year old on the B section first. If he can handle that without complaining I would do the longer A section the next time.
If you park in the lot opposite the Angler Inn and go across the bridge go left insteead of right. Trail starts about 3-5 mins down there.