"Hey, Caterpillar, were you playing with Monica's iPad?"

 "No."

 "Remember last week, when you all were with us and you guys were listening to a book on the iPad?"

 "Yes."

 "Were you also playing around with it?"

 "No."

 "You weren't playing any games or taking pictures or anything?"

 "No."

 "Are you SURE?"

 "Well, maybe she let us play just a little bit... how did you know?"

"Because Mommas ALWAYS know what their kids have been doing."

 ...and this, found later by the owner of said iPad: