It happened at the Barnes and Noble in the Neshaminy Mall on February 10.
They released surveillance photos on Friday of the thief in action.
Police say the suspect stole five boxes of Legos and drove off in a gray pickup truck.
He was wearing a black puffy winter jacket with an unknown logo, gray sweatpants, green/blue sneakers, and a gray Jeff cap.
Anyone with information is asked to contact Bensalem police at 215-633-3719.