What Precautions Should Be Taken To Avoid Fractures In A Child?

9yrs old grandson fell unicameral bone cyst revealed on ex-ray. Arm is broken could not cast as break is too high near shoulder. he has a sling/brace. My question is :is there a way to keep the arm steady and not risk more breaking problems if another fall or bump occurs? Really concerned about school and all the acitivity around him Thanks so much!!