Superior — A 20-year-old mother was being held on Tuesday on a $2m bond on suspicion of first-degree murder after her two children were found dead in car seats inside a car, officials said.The bodies were found outside the family's home in Superior, a historic mining town of about 2 900 people, 97km east of Phoenix.Superior Interim Police Chief Christian Ensley said that members of his department had called Child Protective Services in early January because of concerns about the two children. The state agency said on Tuesday it had received two calls about the children, including the one in January, but had never found evidence of child neglect or abuse.Autopsies were being conducted to determine causes of death of the 2-year-old boy and 10-month-old girl and the Pinal County Sheriff's Office did not immediately disclose what evidence had been found.The mother was identified as Brittany Velasquez, 20. She was jailed and authorities did not know whether she had a lawyer who could comment on the allegations, said sheriff's spokesperson Navideh Forghani. The names of the children were not immediately made public.A $2m bond was set during a Tuesday hearing at the Pinal County Adult Detention Facility. She is scheduled to next appear before a judge on April 30.Foul play suspectedEnsley provided few details during an afternoon news conference, including how the children may have died. He said the mother had made the initial call to authorities. Pinal County Sheriff Mark Lamb, whose office is helping the small town police department with the investigation, said he was unaware of any stab or gunshot wounds to the children.Some relatives of the children were inside the home when authorities went to crime scene late on Monday night but Forghani said she could not provide information about the circumstances of how the children were placed or left in the car or a motive into their killings.She declined to discuss the evidence that was discovered but the sheriff's office said in a statement that it "indicated foul play".During the afternoon news conference, both Ensley and Lamb declined to discuss a possible motive in the case.Ensley said the children's father had died last year and that he knew many members of the Velasquez family.The killings were bound to have a real impact on the tight community, the acting police chief added."This is a real blow," he said. "This doesn't happen often."'No visible signs of abuse or neglect'Ensley said his officers had been called to the home where Velasquez was living in early January to investigate a theft and called the state's Department of Child Safety to report possible child abuse or neglect. He did not elaborate.The state agency said on Tuesday it had received two reports about the children in the past, most recently in early January."The children showed no visible signs of abuse or neglect," the agency said in a response to a query from The Associated Press. "There were no legal grounds to remove the children from the parent's custody."No one answered the door on Tuesday at the run-down, one-story brick house in the hardscrabble community where the car containing the children had been parked.Ensley confirmed that Velasquez's grandparents Lorenzo and Sally lived there and the children had been found in a car parked outside.Broken wooden furniture, cardboard boxes and a rusted barbeque grill littered the brown, dried up grass in the front yard. Two pickup trucks and a car with its hood up sat at the end of dirt driveway. Authorities said the car the children had been in was towed away earlier.Residents of the community established in the 1800s to support a copper mine include retirees and former mining workers. The nearby mine is currently closed but a mining company is trying to reopen it.