Child services visited a Bronx apartment while a 4-year-old girl was trapped inside with the corpses of her troubled mom and brother – but walked away after knocking, neighbors said.

Lisa Cotton, 38, and her 8-year-old son, Nazir Millien, had been dead for at least two weeks before relatives found them and the toddler inside the house of horrors Friday, one day after reps for the Administration for Children’s Services dropped the ball, neighbor Sabrina Coleson said.

“They didn’t do s–t,” Coleson said Sunday. “They were here ringing people’s bells the day before the wellness check. They were here, but they didn’t do s–t.

Promise Cotton, 4, survived on chocolate for at least two weeks after her mother and brother died, her family said.

Lisa Cotton, 38, had a troubled history and an open ACS case for child neglect, law enforcement sources said.

“One rang my bell and asked if I had any concerns for upstairs. And then a man opened his door and started yelling,” she said. “Lisa was a very cool girl. I never saw her son with her, only the girl. It’s terrible.”

Concerned relatives finally checked on the family on Friday and found the 4-year-old, Promise, alone, starving and in horrid condition on her mother’s bed — as bugs crawled over her dead family.

Cotton’s father, Hubert, 71, had sent his oldest granddaughter to check the apartment at East 231st Street — with the woman grabbing her young sibling and fleeing the putrid home to call police.

ACS wasn’t the only city agency to leave Promise trapped in hellish conditions — neighbors said cops were also called to the apartment on Tuesday but left after not sensing the stench reported by others.

Police and ACS both knocked on Lisa Cotton’s door in the days before she was found dead, but both walked away. Hubert Cotton said the toddler survived by “feeding herself with chocolate.”

Law enforcement sources said Lisa Cotton had a history of erratic behavior, and had a pending ACS case for alleged child neglect before she was found dead.

She was arrested in 2021 on child abandonment charges after police said she was caught swinging her then-infant daughter around in a stroller and lighting a wig on fire on White Plains Road, sources said.

Nazir Millien, 8, was born prematurely and required a feeding tube. Sources say he may have starved to death.

When cops arrived she was allegedly walking away, leaving Promise behind. The outcome of the case was not available because the file is sealed.

One neighbor said the mom had “episodes” in the past.

Sources said police believe Lisa Cotton, who suffered from asthma, may have died from cardiac arrest, while her son, who was born prematurely and had a feeding tube, may have starved to death.

A spokesperson for ACS declined to comment on the case on Sunday other than to say the agency is “investigating this tragedy with the NYPD.”