The girls, Domini, 5, and her sister, Dioni, 3, were found just before 3 p.m. Sunday, in front of the Bay View Houses in the city's Brooklyn borough, the New York Daily News reported.
"They gave us their first names and said their mom dropped them off," a police source told the newspaper.
The older girl said their mother left them on the sidewalk with extra diapers.
"Mommy just left us on the sidewalk and drove away," Domini told a Daily News.
The girls told police the street they lived on, but were not able to remember which neighborhood or borough they lived in. They did tell police their mother was driving a white car.
Officers pieced together the mother's identity and arrested Dalisha Adams, 26, in Brooklyn, police said. She was charged with two counts of endangering the welfare of a child.