There's nothing can be done if it's a birth defect. However, you may still try to cast his bowed legs that includes the wrist and keep the brace for at least 3 nights. Also, when the brace is on, help him get used to it by walking him in natural places. Avoid paths that are smooth because some cases of carpal deformity are due to walking/running in smooth surfaces. What I did to Perci was a flattened wood big enough to cover her legs and wrapped it with cotton and gauze. A very strong cardboard may do as well. Just make sure it doesn't bend. I haven't tried commercially available cast so I cannot say how effective they are.