Why?

Why do kids do this kind of stuff? Today while Mady was at school Bella thought it would be a good idea to smear butt paste all over her bathroom. Why?  she said " the bathroom had a rash" What you can't see is the butt paste is all over the tooth brushes, toilet, and sippy cups. ( why there is a sippy cup in the bathroom, I have no idea) I really need to have 12 arms and at least 6 eyes. I am just not used to this big house. I can't hear anything going on upstairs.