Two young children died of heat exposure in cars over the Fourth of July holiday while playing with their siblings.

In Omaha, Neb., a 2 1/2-year-old boy died Monday after his 5-year-old brother helped him into a car, shut the door and went off to play.

Authorities don't know how long Arnold Guzman was in the car before his mother found him. The windows were rolled up and temperatures inside were over 100.

``A 2 1/2-year-old can't easily get out of the car, and the kids were apparently playing in the backyard and forgot about him,'' Police Sgt. Dan Cisar said.

In Masontown, Pa., on Sunday afternoon, a 2-year-old boy died while ducking down in the passenger seat of the family car during a game of hide-and-seek with his older sisters.

When Cody Anthony Britt's sisters, age 6 and 3, could not find him, the family began searching for him. At first, the family looked in the car but did not see him. On a second check of the car, they opened the passenger door and the boy tumbled out.

Cody had been inside the car for at least an hour, with outside temperatures in the high 90s, and the boy's asthma condition made the heat particularly dangerous, Fayette County Coroner Phillip Reilly said.

Both deaths are being treated as accidents.