Dowlan installed a little lock at the top, even higher-up than they could reach on a chair, stool, or anything else they could drag over.
He considered one of those latches that automatically latches every time a door is shut. I asked him, "So how do I get back out when I'm done?" To which he replied, "Oh, yeah."
He installed it while the kids were sleeping. So the first time the girls try to open it, they get indignant. "Mommeeee! The door to the room that we aren't supposed to be in won't open!"
And you're telling me this because . . . ?
They conceded defeat in their epic struggle of knob vs girl and have moved on to destroying other portions of the house. Until they discovered the great flaw with the manual latch: that the man will never latch it when he's done in the room.