A Bronx mother says the death of her 4-year-old daughter who fell out of a window on Saturday was a tragic accident.

The incident happened around 5 p.m. on East 140th Street. Police say the girl, Helena Flores, was in an apartment with at least two adults when she walked fell from a window and fell four stories.

Her mother, Hilda Flores, says it happened despite extra precautions because her daughter had autism. "One mistake changed all this in a split second," she says.

Helena had only just turned 4, and Sunday was supposed to be the day of her birthday party.

Flores says she was napping Saturday afternoon while her sister watched the kids as they played between the living room and bedroom.

When Helena went silent and her aunt couldn't locate her, she woke Hilda. They looked out of Helena's bedroom window and saw the child on the ground below.

Hilda Flores says two radiators in the bedroom often left it sweltering. She says the top window was typically left cracked open about 2 inches.

The mother says Helena found a way to climb up the window and open it wider, then fell out. She says her daughter "died on impact."

"Although no amount of words could console my family and I, knowing she didn't suffer gives an inch of peace," she says.

Flores says there are window guards on the bottom window, but they don't reach high enough to cover the top window that Helena fell from. She says the Administration for Children's Services has asked her family to vacate the apartment until the landlord cane place some sort of lock on the window to prevent another tragic accident.