This is a sleep positioner used for babies in the NICU, it helps to support their bodies, mainly their hips and legs. My family is expecting a new one this Match with Osteogenesis Imperfecta and he has already broken each femur, these provide the perfect amount of support for their little legs. I spoke with a couple of the local ER nurses and they think that these would be greatly appriciated by the NICU folks.
The link also provides ideas about how to use it. I found the poly pellets needed for the inside at Micheals in the doll craft section for about $10 and used a 40% coupon with it. I believe Joann's carries it too.