It happened around 5:15 p.m. Friday at Childcare of the Future, located on the 700 block of Secane Avenue in Primos.
In a news conference Monday evening, Upper Darby Police Superintendent Michael Chitwood said 52-year-old Sarah Gable of Folcroft pushed the little girl down a flight of steps.
A camera, installed just a half hour before the incident, captured it all on video.
Watch surveillance video released by police:
In the video, you can see the girl enter the picture at the top of the steps, when for seemingly no reason, Gable approaches from behind and shoves the girl down approximately six steps.
Gable then follows the girl down the steps, helps her up and then looks squarely at the camera.
Luckily, the girl was not seriously injured.
"When parents give their kids to day care centers, the expectation is that their children are going to be taken care of," Chitwood said.
Police say as soon as the day care owner discovered the video of the incident, Gable was confronted and police were contacted. She was then fired from her job at the day care.
Gable is now charged with simple assault, harassment, and endangering the welfare of the child. She is now free on $25,000 secured bond.