An 8-month-old boy died Friday after he was apparently left in his mother’s car while she was at work, Alexandria police said.

The exact cause of the child’s death was not immediately known, but the temperature reached 90 degrees at Reagan National Airport.

Typically, temperatures inside cars with closed windows rise well above the outdoor temperature.

Alexandria police said they were called to Inova Alexandria Hospital after an unresponsive child was brought there just after 4 p.m., said Lt. Mark Bergin, a police spokesman.

According to Bergin, hospital staff were told by the child’s mother that the boy was in the car when she left her home in Alexandria in the morning for work in Arlington County.

Bergin said the mother intended to drop the child off at day care. It was not clear why she did not.

He said that as the woman was driving home, the child was still in the car.

He was unresponsive and was taken immediately to the hospital, Bergin said.

Neither the woman nor the child was identified.

Police in Arlington and Alexandria said the investigation would be conducted by Arlington police.

Arlington police provided no additional details.

Also on Friday, Baltimore County police said a toddler died after being left in a vehicle in Lansdowne, police said.

A relative was supposed to take 16-month-old Sabriya Towels to a Head Start Center on Friday after picking her up at another location but instead drove to their home in Baltimore, went inside and slept for a few hours, police said.

Police said that about four hours later, the relative, who was not Sabrinya’s parent, went to the Head Start Center to pick up the toddler and realized she was not there. He then ran to his vehicle and found the girl inside.

That case was referred to the State’s Attorney’s Office for review, police said.

The Web site Kids and Cars. org said that on average, 38 children die in hot cars each year after being trapped inside.

“Even the best of parents or caregivers can overlook a sleeping baby in a car,” the Web site says.

In an earlier incident in the Washington area, a woman from the Bristow section of Prince William County pleaded guilty last year to two misdemeanor charges of child neglect in connection with the 2011 death of her toddler son, who had been left in the family minivan for about seven hours.