While a mother briefly turned her back to the 1-year-old son she had just put in a child seat, someone hopped into the running car and took off with it Thursday, police in Philadelphia said.

The car with the unharmed child was found a few blocks away about 40 minutes later. Police are searching for a suspect and are investigating it as a kidnapping.

The mother put her son in the back seat but had to run back to the house to get something she had forgotten. The car was driven off.

“We believe that since the vehicle’s engine was running, someone saw an opportunity to steal the car, didn’t realize that there was a 1-year-old child in the back seat,” said Chief Inspector Scott Small.

“We’re lucky that 1-year-old child is OK and reunited with the mother, so it’s actually a happy ending,” Small said. “The lesson learned here is don’t leave your engine running, especially if you have your child in the back seat.”