The video, taken by Bronx resident Jennifer Mares on Saturday evening, shows the child in a diaper clinging onto the window where the 3-year-old boy had just climbed out. Several people below could be heard gasping and urging the child to go back into the residence.
Mares told ABC News that she was with her son at a park outside their apartment building when she heard someone say a baby was in the window. She called police and began filming the incident, but fearing they wouldn't arrive in time, she counted the number of floors and ran into the building, she said.
Mares found the apartment where the toddler lives and banged on the door, which was answered by the child's mother. The child's 14-year-old sister then grabbed him and brought him inside, Mares said.
The boy's mother, who was not named, told New York ABC station WABC that he snuck out while she was making dinner. The boy had pushed the air conditioner aside and crawled through the gap, his mother said.
The mother, who immigrated to New York from Mali, said other residents have been calling her names and telling her she will go to jail.
"God saved my boy, and he will save me from these people," she told the station.
The New York City Administration for Children's Services is investigating the incident, a spokesperson told WABC.
Officials went back to the apartment the next day after receiving reports that the boy had climbed outside the window again, but the mother insisted that bars installed early Sunday morning would have prevented another escape from occurring, according to WABC.
ABC News' Rachel Katz contributed to this report.