The Florida reality TV mom whose unsupervised 6-year-old fatally pummeled his infant sister was already under investigation for abuse, according to reports.

Child protective services in Florida were knocking on Kathleen Steele’s door just three days following the July 26 birth, after Steele took the baby girl to the hospital with a head injury, the Tampa Bay Times reported.

The baby had bleeding on the brain, doctors said, but investigators found no evidence of abuse, according to the newspaper.

Steele claimed the baby was hurt after she fell out of her carrier when the mom — who once appeared in the show, “I’m Pregnant … and 55 Years Old” — tripped on the stairs.

Authorities were set to follow up on Aug. 1 but Steele, now 62, rescheduled — and in the meantime, the infant died brutally at the hands of her older brother, cops said.

Steele was charged with manslaughter after leaving the boy alone in a van for 30 minutes last week with his 3-year-old brother and infant sister, who began crying, prompting the boy to try to comfort the baby.

Instead, the boy repeatedly struck the baby, causing catastrophic injuries which killed her.

The mom appeared in court Friday and was released on $100,000 bail.

A judge placed Steele under house arrest, required her to wear a GPS monitor and to stay away from kids.

After appearing on the reality show, Steele used her dead husband’s sperm and in vitro fertilization to have her two youngest kids.

The family had already been thrown into disarray by a fire at their home just days before the baby girl was born, neighbors said.

Steele’s attorney said the mom was “certainly devastated” by her daughter’s death, but police painted a different picture of the “aloof” woman, who allegedly said, “I guess I have to plan a funeral,” hile authorities questioned her about the baby’s death.

The 6-year-old used a doll to show police how he brutalized the baby inside the family van, where investigators found blood on the ceiling, according to reports