S.H.
If you do a Google search on "spica casts" or "what is a spica cast" or etc., lots of sites will come up... and give you tips.
And the care of it etc.
Perhaps, you can ask the Doctor.... and maybe medical supply stores, might have something for a child in this situation...
Here is a link for example:
http://www.uihealthcare.com/topics/medicaldepartments/ped...