Smith family joke for kids

The Smith family is a very wealthy family that lives in a big, circular home. One morning, Mr. Smith woke up and saw a strawberry jam stain on his new carpet. He figured out that everyone who was there that morning had a jam sandwich. By reading the following excuses, figure out who spilled the jam.
Billy Smith: "I was outside playing basketball."
The Maid: "I was dusting the corners of the house."
Chef: "I was starting to make lunch for later."
Who is lying?
A: It was the maid. The house is circular, it has no corners.