Two of your subordinates often provide their children with school supplies from the office. how do you handle this situation?

This is the answer I'd pick - Send a notice to all employees that office supplies are for office use only and that disregard will result in disciplinary action.
The reason for this is because it would solve this problem that has occurred at the moment, as well as any other potential future problems as well. The employees will now know they shouldn't take office supplies home, and those who did will stop doing so.