Police on Monday evening located the mother of a 4-year-old girl who had been found earlier in the day wandering alone on a south Brooklyn street, cops said.

Authorities found the kid walking alone at about 9 a.m. on Shore Parkway and 27th Avenue near Calvert Vaux Playground in Gravesend, police said.

Investigtors believe she slipped off a school bus after the driver and another worker let off other children, but did not check to see if the bus was empty.

When the driver of the bus parked, the little girl wandered off the bus alone, cops said.

Police then reviewed surveillance videos in the area and traced the bus back to the school, authorities said.

From there, they identified the girl’s mother, who picked her up at the 60th Precinct station house in Coney Island.