My son has a broke forearm, any guidance

*Reasked the question because the X rays weren't attached last time* My 16-year old son fractured both bones of his left forearm while playing football. The doctors reduced/re-aligned the fracture and put his arm in a plaster cast. We have attached the X-rays after reduction. We have been advised to get another X-ray after one week to check whether the bones remain properly aligned. If they have shifted, surgery with plates may be required. We really do not want surgery and would like to avoid it unless it is absolutely necessary. Based on the X-rays, does the alignment after reduction look satisfactory, and is there a reasonable chance that the fracture can heal naturally in the plaster? What precautions should we take to prevent displacement, and what is the correct position for the arm while sitting and sleeping? Also, is a full recovery with normal movement expected at his age? Any guidance would be greatly appreciated.