The two were sitting in a parked 2001 Honda Civic in a lot behind Toto's Pizzeria and Restaurant at 1250 El Camino Real at about 9 p.m. when a man wearing a black windbreaker and jeans got into the car and demanded the keys, according to Belmont police.
He pushed the woman out of the car, but she managed to pull her daughter from the backseat before he drove away, police said. No weapon was seen, and the mother and child were unhurt.
Responding officers were unable to locate the carjacker.
However, at about 2 a.m. today, a California Highway Patrol officer spotted the Honda Civic stopped on the side of U.S. Highway 101 near Broadway in Burlingame.
Stephan Thomas Allen, 20, of Rohnert Park, was inside the car and was arrested on suspicion of carjacking and booked into San Mateo County Jail, police said.
"He did give us a statement during which he admitted to taking the car," Belmont police Capt. Dan DeSmidt said.
Belmont police are in contact with other local law enforcement agencies to determine whether Allen may have been involved in other crimes on the Peninsula, he said.
Anyone with information on the case is urged to contact the Belmont Police Department at (650) 595-7400.