Brake in Growth Plate?

Last night y son (8) fell skateboardingng and hurt his wrist. Went to ER and to EVERYONES surprise no brake was shown on the X-ray. Doctor says he has a break in his growth plate. They put him in a soft cast wih a splint and the pain did get better but he is swollen and still hurts and needs the pain meds they gave him. How serious is this injury and should he be abe to move his fingers without pain? Please help!!