Children are not responsible enough to have a ferret as a pet. The ferret needs to be trained to not bite people. There is lots of text on that subject here and on the internet (search for "ferret bite training"). You never hit or flick a ferret's nose for bad behavior.
If the child is not old enough to know how to correctly stop a ferret from biting, He (or she) should not be in the presence in the same room as a ferret (or any other animal)
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If the wound is small and shallow - rinse the wound thoroughly with water. Dry the wound. Put antiseptic on the wound. Bandage the wound if necessary Contact your doctor or hospital as soon as you can.
If the would is deep and bleeding a lot - sit down and raise the wound above the level of your heart. Apply pressure to the wound. Go to your doctor or hospital as soon as possible.
Depends on how hard the ferret bites. They have powerful jaws and sharp teeth that doesn't take much to puncture human skin and it hurts.