The position on the knees on W (or 鈥淭V sitting鈥? presents orthopaedic inconveniences but is very interesting for the activities on the ground. Considering the importance of their disorders, some children PC (IMC very affected and all the more the multi-handicapped) cannot adopt this position. The 鈥渕otorcycle鈥?is a foam device, which is inspired of 鈥渢rotte-lapin鈥? to which is added a thoracic support. It allows the children very affected in their motricity to reach the activities on the ground in comfortable and active situation, even in the company of other children, valid or less affected: the thoracic support helps the relaxation and the mobility of upper limbs 鈥撀爄n connection with the visual activity聽鈥?while allowing the emergence of the antigravity response of the axis of the body. The 鈥渕otorcycle鈥?can be considered as a supplement to the various installations and the reeducational situations.