Is it obligatory to dispose of the money found by the son in his backpack, which was used to carry items during relocation, knowing that the amount was found in an outer pocket, wrapped, and it is feared that someone else might have put it there by mistake?

The basic principle is that the money found in a belonging is the property of its owner. However, if there is doubt about the source of the money, the son should ask his schoolmates. If someone claims the money and describes it accurately, it must be returned to him. If no one claims it, then it can be given as charity.