Trail Map
Look at the attached map, you can see that the blue route crosses the main fire road tracks multiple times, as such it is super easy to bail at any point and head back to the main centre.
Because of this, dont worry about what other peoples kids have done and at what age, just rock up and go for a ride, if they find it too hard bail out on to the fire road for a ride.
most obvious “cheat” is at the end of blue 5 (i think) is go straight on instead of left, cuts out a bit of singletrack, but it also cuts out a short steep grunty climb. it is not hhard or long, but for my youngsters they came off a downhill, wrong gear, then failed… missing it kept the flow and the next time they were much more confident.