A Las Vegas mom and stepfather are accused of hiding one of their dead children in the garage and abandoning their daughter, pregnant with her stepdad's child, at home for months at a time.

Jondrew Lachaux and Kellie Phillips were charged with child abuse among other allegations after they turned themselves over to North Las Vegas police, the Associated Press reported Wednesday.

Before the arrests, their 3-year-old daughter was found dead in a box in the back seat of a broken-down Mercedes.

The body was badly decomposed, wrapped in blankets, bags and pizza boxes, according to court documents obtained by the AP. 

Investigators say the harrowing and complex case of child abuse goes back at least a year, when 39-year-old Lachaux and 38-year-old Phillips took five of their seven children with them on a road trip from Las Vegas to California.

They left behind their sickly 3-year-old and a teen girl, who is Lachaux's stepdaughter, because there was no room in the car, court records say.

At home, the teen struggled to take care of her little sister while dealing with her own pregnancy, believed to be the result of Lachaux raping her without Phillips knowing.

She gave birth to a baby girl alone at home and without medical assistance. The food and medication her mother left eventually ran out, but she told investigators she was too afraid to call for help.

"The evidence is leading investigators to believe she was almost a prisoner in her home," Sergeant Chrissie Coon told the AP. "Fugitives can psychologically confine their victims without physically being present." 

The 3-year-old's condition worsened until she had trouble breathing and died sometime in early March, according to her teen sister. She said it took two weeks before her parents returned her phone calls to tell them the child had died, the AP reported.

When Lachaux returned, he allegedly hid the body and then kicked his stepdaughter out of the house to prevent her from telling Phillips about her newborn.

The teen wandered around homeless for several days until she and her infant were found April 1 at McCarren International Airport. The infant is being hospitalized for starvation and hypothermia, and her mother is also facing child abuse charges.

Lachaux is officially charged with child abuse with substantial bodily harm or death and attempting to destroy and conceal evidence, KLAS-TV reported. Phillips faces the same child abuse charge. The rest of their children, ages 1 to 9, are now in protective custody.