Where did they come from?

My children are insane. They were making a bunch of noise during their "nap" yesterday, so Chris went in to see what they were doing. I heard silence when he walked in, followed by, "Go show Mama." That's never good. David and Henry both came walking out into the living room with black marker ALL OVER themselves. Henry looked like one of the prisoners in a documentary with prison tattoos all over his face. He also had his back, legs, arms, and feet marked, and even his belly button colored in! David had slash marks all over his legs and arms, and even on the bottoms of his feet. They wrote on the carpet, drapes, dresser, each rung of the ladder on their bed, Henry's sheets, the train table, the tv cabinet, their cups, and the door to their closet. Thankfully it was a dry erase-type marker from a book they have which had been mistakenly put away in their toy box instead of put in the closet. It came off of everything easily, but we haven't attempted the carpet yet. I'm sure we'll be able to get it out though. At this point we have master carpet cleaning skills. And the worst part is that my camera is broken so I couldn't even take pictures of it!!! We got it on video though, and if I can figure out how to upload it I will. I was laughing so hard they kept saying, "Mama, why you crying?" It was so hysterical I couldn't be angry!