The five-year-old and three-year-old are not old enough to see over the steering wheel and their feet cannot even reach the pedals. But they somehow managed to start the engine and drive the car into a nearby intersection where they T-boned a second vehicle.
The Federal Way Police Department posted photos of the damage on their Facebook page.
Neighbors heard the crash and ran outside to see what happened.
"(It sounded) like and explosion went off -- something, we really don't know. So I ran out and I saw it," neighbor Annemarie Warren told KOMO-TV. "I knew it was our neighbor's car, but I did not know she wasn't in the car. Only the two little ones."
The children were uninjured, witnesses said. The driver of the second car had cuts and bruises.
"I held the kids both in their hands and I said, 'where's your mom?' (They said,) 'sleeping. I want to go to my grandma's house,'" said Warren. "I was waiting for the mother to come out, too, you know?"
Authorities did not say whether the parents could face any charges.