Ruby Rose says she was accused of killing a 4-year-old child when she was a teenager … with her peers even referring to her as “Baby Killer.”

The actress told the shocking story on an episode of Kaitlyn Bristowe‘s “Off the Vine” podcast — released Tuesday … telling “The Bachelorette” star she snuck off from a party to smoke her first cigarette with a pal when she was 15, and they spotted an odd shape in the bushes at a playground.

Ruby says she and the friend went to investigate … and found a badly injured 4-year-old boy lying in the bushes with “blood coming out of his ear, nose, mouth.”

She says she and her friend picked up the child and took him back to the house where the party was going on … and the adults started performing CPR.

The kid was rushed to the hospital …. but Ruby says he ultimately died — and cops came to her school to talk to her about it.

While they decided she’d done nothing wrong, her fellow classmates weren’t kind … and she remembers being berated by calls of “Baby Killer!”

Ruby says the child’s brother had suffered dissociative amnesia due to the traumatic incident … but later remembered what happened and spoke to cops. The family, however, did not want Ruby at the funeral.