MIAMI - A six-year-old boy beat to death his 13-day-old sister after their mother left them alone in her van for more than half an hour in west Florida, police said.

The mother, 62-year-old Kathleen Marie Steele, appeared in court on Friday and was charged with aggravated manslaughter and neglect in the infant’s death, the Tampa Bay Times reported. Bail was set at $100,000.

Pinellas County sheriff Bob Gualtieri said Steele took her three children - Frankie, 6, Philip, 3, and 13-day-old Kathleen - with her while she ran errands in the Florida city St Petersburg on Monday.

Steele had conceived the newborn through artificial insemination and appeared on a reality TV show called, “I’m Pregnant and 55 years old.” She went into a store for nearly 40 minutes, shutting the children inside the minivan with the windows and doors closed, Gualtieri told journalists.

After the baby began to cry, Frankie took the infant out of her car seat and “began flipping her, multiple times back and forth, dropping her around the floor, slamming her head against the ceiling, striking her in the face and causing severe trauma,” Gualtieri said.

When Steele returned from the store, her son told her what happened but she decided to continue with her errands, not returning home until two hours later. By then the baby was blue and cold to the touch. Steele contacted a neighbor who was a nurse, who called 911, according to the sheriff.

The baby was taken to a clinic where she was pronounced dead. “Those of us who have been doing this in this business for a very long time have never seen anything like this,” Gualtieri said.

He said the boy, who will not be charged, used a doll to describe to police what he had done. “By numerous witness accounts, Kathleen Steele was an inattentive parent and Frankie and Philip were largely unsupervised and had very serious behavior issues,” the sheriff said. “Frankie is a victim, he has a lot of issues and a lot of problems.”