The parents come back home, see the living-room is in a terrible mess.
Do they ask their little ones "What have you done?" or "What have you been doing?"
What is understood in each of the questions?
I call this a tricky case because the usual criterion to distinguish between Present Perfect Simple and Present Perfect Continuous, the focus on the result of the action for the simple, and on the action itself for the continuous is a bit difficult to use here, isn't it?