A Texas mother has been arrested after she told police her two children died in a hot car, but authorities have found 'inconsistencies' in her story.

Tiona Islar, the mother of six-year-old Sevani Stevenson and three-year-old Miyani Islar, told police she last saw her children alive in her San Antonio area home around 10am on Saturday.

Islar said she fell asleep and found the children in her car around 3pm before bringing them inside, according to Bexar County Sheriff Javier Salazar.

The mother added that the siblings must have made their way outside and somehow gotten into the car.

She called police around 3:25pm and a deputy arrived who tried to perform CPR on both children at the same time.