Think of it this way,
If I personally sent private mercenaries and bounty hunters to your house who were told that you and your family members were dangerous criminals armed with high-powered weapons, and they broke into your house and held your family at gunpoint in the middle of the night, what punishment do you believe would be appropriate?
Or, imagine that I broke into your house in the middle of the night with several of my friends, armed to the teeth, and held you and your family members at gunpoint. If nobody was permanently (physically) injured or killed, would you still consider that a "harmless prank"?
As a point of simple logic, try putting yourself in their shoes.