As soon as your child has mastered walking, they are big enough to go hiking . Our son was 3 when we started hiking with him. The first time we went we took a wagon so that if he was tired, he could ride. Well, there was no way he riding; he was pulling and did so for the two mile hike (an asphalt trail in the Smoky Mountains). We went several times that year and hiked a lot of the easy trails at a very easy pace. He enjoyed playing the three bears in the woods. Baby bear loved to walk and balance on the fallen trees. He loved to jump off the big rocks (big to him) and he took it upon himself to clear the trails of all the fallen limbs and still does this today. He enjoyed throwing rocks in the creeks.
This sport is more than just fun - it also gives the opportunity to practice those therapy exercises. Climbing up the trails stretches the foot and leg muscles and coming down the trail uses another set of muscles. Walking on the fallen trees in a challenge in balance and throwing the limbs off the trail has use of both hands for the larger ones.
Watch for balance problems when descending on steep trails. Some national and state parks will have maps giving the distance of trails. Ask how accessible the trails are for people with disabilities. You can check out accessibility online by going to the website for each national park.
Start with short hikes and gradually build up as your child has more strength and stamina. Remember to take lots of water and protect the child from the sun. A cell phone and the number of the camp office is a good idea if your child has epilepsy. – Ron