Jose Hernandez, 27, and Vanessa del Pilar Martinez, 20, were arrested for the robbery Monday, the Los Angeles Times reported.
The two allegedly pulled up to the crossing guard's intersection and began to turn the corner. The guard lifted her stop sign higher in the air and said, "You have to stop, the children come first."
Witnesses told detectives Hernandez yelled at the guard that he was not stopping. Meanwhile, they said, Martinez left the passenger seat, approached the guard as she tried to walk away, started hitting her with her fists, and knocked her to the ground.
Hernandez then took the guard's stop sign while Martinez took the guard's lanyard with her whistle and work identification from around her neck, police said.
"We have never seen anything like this before and hope we never do again," sheriff's Lt. Mike Thatcher said.
The two suspects drove away, but adults at the scene provided information, including the license plate number, leading to the arrest, the Times reported.