Updated at 9:10 p.m.: Revised to include the victims' identities.

Two toddlers died Friday after their mother says they locked themselves inside a hot car in Weatherford.

The children's mother called authorities around 4 p.m. to report that her 2-year-old daughter and 16-month-old son "took off," the Parker County Sheriff's Department said.

The woman searched the property for the children and found them locked inside a small four-door vehicle. She said they had gotten into the car on their own and locked themselves inside.

The temperature at the time was 96 degrees.

The mother broke a window to get to the children, who were unresponsive, and emergency crews were sent to the scene in the 200 block of Rambling Loop.

The children, identified as 2-year-old Juliet and 1-year-old Cavanaugh Ramirez, were pronounced dead just after 4:30 p.m. The Tarrant County medical examiner had not determined a cause and manner of death for them.

Sheriff Larry Fowler said the case, which he called "especially heartbreaking," was in the early stages of investigation.

More than 700 children have died in hot cars in the U.S. since 1998 — including 107 in Texas, not including Friday's — according to noheatstroke.org, which tracks such deaths. Seven Texas children died in hot cars in 2016, including two in North Texas.

The Weatherford deaths are the second and third in North Texas this year. Kingston Jackson, 1, died in April after being left for up to five hours in a car in Burleson.