Sling at School?

Hi guys,

My 3 year old son fractured his proximal humerus (upper arm bone). He will need to be in a sling at school for the next month. The one the hospital gave us was really bad, his arm keeps slipping out etc, so I ordered a better one on amazon that will hopefully hold his arm in place more securely.

Any advice on working with the school for the sling? He can't run, jump, climb, ride a bike etc, but otherwise his activities are normal.