 This is a randomized controlled open trial open with a stratified distribution. Children will be randomized between two arms - Arm A Experimental - Immediate Program: the child follows the physical activity program for a period of 18 months, as soon as his medical condition permits. - Arm B Control - Delayed Program: the child does not participate to the program during the first 6 months, and he joins the delayed program late after 6 months. Each child integrates the physical program for a period of one year. 