The former star of the reality TV show "I’m Pregnant and 55 Years Old" was arrested Thursday after her 6-year-old son killed his infant sister while the children were left in a hot car, deputies said.

WTVT reported that Kathleen Marie Steele, 62, left her three children in a car on Monday while she ran into a cellphone repair store in St. Petersburg with the windows of the vehicle rolled up and the engine turned off. Deputies said the infant began to cry, and the 6-year-old "slammed the baby on the ground and flipped her around."

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"The best way I can describe it is, he pummeled her," Pinellas County Sheriff Bob Gualtieri told WTVT. "We decided not to charge (the 6-year-old). But nonetheless, we have a 6-year-old who killed a 13-day-old."

The baby "suffered several injuries including a fractured skull, cuts, and bruising," deputies said. Blood was found on the ceiling of the van.

When Steele returned to the car, the boy said the baby was hurt but she ignored him and didn’t call 911 until they got home.

"Deputies are there, paramedics are there working on a 13-day-old baby who's obviously dead," Gualtieri told Bay News 9. "And she turns around and goes into the kitchen and starts putting groceries away. Who does that?"

Steele's husband died of cancer in 2011, according to the Tampa Bay Times. The couple appeared on the reality show "I'm Pregnant and 55 Years Old" in 2009. Steele had her youngest two children as a result of artificial insemination with her dead husband's frozen sperm.

She was charged with aggravated manslaughter of a child.