Beaverton Police Spokesman Officer Matt Henderson told CNN when the car thief saw the child he returned to the mother and threatened to call the police on her for leaving the child in the car.
"He hopped in the car, drove it, realised there was a 4-year-old inside, and drove back and ordered her to take the child out of the car and then drove away again," Henderson said.
"We're thankful he had the decency to bring the little one back."
The young boy was unharmed and returned safely to his mother.
However, when the child was returned, the thief gave the mother a lecture because she had left her son in the car unattended. He also threatened to call the police on her.
"As moms, we get really busy and we think we're just running in for a second and this is just a perfect example of just letting our guards down and how terrible it could have ended," Leary, told KPTV.
"I am thankful that he is okay. It was so stupid and I'll never do that again, but it's that split-second decision that can just change everything."
While the incident was unfolding Leary was just a few metres away, however, she turned around at the wrong moment.
The stolen vehicle was found a few hours later.
Police are still searching for the thief.
"This is a good learning lesson for all of us who have children," Henderson said.
"Be extra careful with your kids, take the extra step to make sure they're safe."
