My niece, who is now 6, had the spica cast. A good friend of ours has a baby 2 days younger than our cranio baby. She is in her second and final spica cast. The first was pink and now it's purple. She has had a time trying to get things to work for her. She bought a Johnny Jump-up that hangs from the doorway and cut 2 slits on the side and put super strong velcro, that way she can be upright. Our 4 yr old daughter wore 3 different casts for 3 months at a time for scoliosis last year. She is now is a removable brace. It's overwhelming a little at first but you get into a routine of sponge baths and special diaper changes. My friends daughter wears a newborn size place inside the cast and a size 6 on the outside.
Good luck with this, if you have any questions feel free and ask and I can ask my sister in law or my friend :)