Sorry to hear this news.
A couple of years ago our GS (9) was at a friends. His buddy same age had a dirt bike. You guessed it, poor kid broke tibia and fibula. It happened the week before school was out for the summer. He got all ok the week wbefore school started again. It was a long summer for him.
Your son will be okay once he gets a walking cast. The hard thing GS found was keeping sand out from inside his cast, between toes. We put a sock just over his toes when at the beach.