Rebounding is a great way to clean the lymphatic system. Do you have a trampoline or a small rebounder. This would be play for a six year old and good for the whole family. You might also incorporate dry skin brushing into his nightly routine. Buy a natural bristle bath brush with a long handle, you can get one for as little as $0.94 at Walmart although there are much more expensive ones available. Gently brush the skin toward the abdomen to move the lymph to where it can be eliminated. There is complete information on the Lymph cleansing forum.
For colon cleansing I believe that Dr. Schulze makes a formula for children. Ideally, a diet with high fiber whole grains and fruits should work, but if his peristalsis is weak, he may need a mild herbal laxative to begin with. A diet low in mucus producing food is vital. Hopefully he will be able to adapt to more veggies and fruit and not depend on meat, dairy and processed foods for the bulk of his food.
I've seen your posts in other forums and hope you can find a natural way to ease your child's problems.