A mum "left her two toddlers to die in a hot car", even when she could hear their cries.

Last Wednesday night, 19-year-old Texas mother Amanda Hawkins, allegedly left her two toddlers inside her car while she spent the night at a friend’s house.

Two-year-old Addyson and Brynn, one, were left inside the car without food or water for 15 hours, KSAT reports.

The two girls were not removed from the car until midday the following day, when outside temperatures reached upwards of 26 degrees. The girls died in hospital the next day.

It's alleged the children could be heard crying by other partygoers, including a 16-year-old male friend, at the house where Amanda was staying, but she refused to bring them inside.

"One of them even told [Amanda] they could hear the kids crying out in the car and told her to bring them in, " Kerr County Sheriff Rusty Hierholzer said.

"She said, 'No, they're fine. They'll cry themselves to sleep'."

When Addyson and Brynn were finally brought inside, they were already unconscious.

"They took the kids in the house, tried to bath them. From what I understand, [the girls were] pretty well unconscious," Hierholzer said.

Friends finally convinced Amanda to take her children to the local hospital, but she told doctors both girls had collapsed while smelling flowers in a park.

Investigators soon determined the real reason for the girls injuries, but they could not be revived and were taken off their ventilators the following evening.

Amanda was charged with child endangerment, but her charges could up be upgraded following the girls' deaths.

Miriam Davis, a former friend of Amanda's, told KSAT she once considered calling Child Services over the treatment of the girls and now regrets not doing so.

"I guess I just hesitated for so long. I didn't want her kids to be in the system, but I didn't know they would die if they didn't," she said.

"If anyone feels something's not right, they need to call [Child Protective Servies], because you don't want two kids to die. It's just not fair.

"Addy was so helpful. She would like to go get you things and bring 'em to you. Brynn was just learning how to walk and she was toddling all over the place."