This requires a little setup but it was funny.  We were eating breakfast and my youngest ran to the fridge and grabbed a bottle of Gatorade.  We asked that he share it with his brother and he agreed.  His brother got up to grab a cup, grabbed the last one in the plastic sleeve and left the plastic sleeve sitting on the counter.  My wife told him to put it in the trash and likened it to the boys grabbing the last item from a box in the pantry and leaving the box there.

With that statement my youngest got up from the table and began to walk into the kitchen.  We asked him where he was going and he said “to get some empty boxes out of the pantry”.  Yes, he knew they were there, he knew they were empty and he knew he was guilty!  They Know!