Hello, your child needs to be evaluated by a specialist in Pediatrics ( and Neurology) for diagnosis of possible muscle and nerve problems. Some of these diseases are called muscular dystrophy or guillain barre. Was your son normal at birth and then delayed at 12 months when he was learning to walk? or has this problem been lifelong? Does he/she have normal cardiac and respiratory function? Sometimes there can be infections and responses to the infection which can cause this problem as well. I would urge you to find a good pediatrician at the largest hospital in your area who will refer you for further evaluation.