An 8-month-old boy died Friday after a Virginia mother forgot he was in her car and went to work, leaving him there all day as temperatures rose to around 90, police said.

The woman drove to her job in Arlington on Friday morning, police said. When she left work Friday afternoon, she discovered she had left the baby inside the car and drove to INOVA Alexandria Hospital just after 4 p.m., Alexandria Lt. Mark Bergin confirmed. The child was pronounced dead at the hospital.

Temperatures in the Arlington area hovered around 90 on Friday. Bergin said Arlington police would investigate the case because it is believed the child died in that city.

Meanwhile, a 16-month-old girl died in Baltimore after being left in a truck by a relative who forgot her when he went home to take a nap, NBCWashington.com reported, citing police.

The relative was supposed to drop the child off at a Head Start center in Baltimore on Friday afternoon but drove home instead. Police say that four hours later he got in his vehicle and drove to the Head Start center to pick up the child, NBCWashington.com reported.

After he was told the child hadn't been dropped off, he found the girl unresponsive in the vehicle. She was pronounced dead at a hospital, NBCWashington.com reported.

Temperatures in Baltimore were in the high 80s on Friday.

Bergin told NBCWashington.com that parents of young children should be extra careful during hot summer months.

"Slow down and be careful ... try not to let things get too busy," he said.