Hawks are migratory, chances are that the situation will right itself without resorting to any illegal acts. If even for a couple of weeks you keep your birds in a covered run the hawk will probably move on if there is no access to easy prey. Others here have tried to encourage crows, as they warn birds of hawks and will chase them off, as well. If you haven't already, you should try to provide as much coverage/hiding spaces for your birds as possible if a covered run isn't possible.
Again, I would not recommend any illegal acts, the last thing your family needs is a hefty fine or an arrest.
I know it's a traumatic event, I am sorry for your loss and that your child witnessed it.