Square pants

Yesterday's conversation ...

Jack: "I want to wear my square pants. Where are they?"

Me: "What square pants?"

Jack: "The ones Grandma gave me."

Me, thinking that the pants Grandma gave him for Christmas must have squares on them: "They're in your closest, I saw them yesterday."

Jack: "No, the square pants that don't go all the way on my legs."

Me: "Oh, I see, square pants."

Square pants = Shorts. Thanks, SpongeBob.