A Utah mom and her three-year-old son were reunited today after the toddler assisted police in finding him after someone stole the car while he was inside, authorities said.

The child's mother, Elizabeth Barrios, said she left her son in the backseat with the car running while she dropped an infant off at daycare.

Elizabeth Barrios says she left her son in the backseat with the car running while she dropped an infant off at daycare.

"I went outside and my car was driving away with my 3-year-old in it," Barrios said.

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Ogden Police Lieutenant and Watch Commander Tim Scott said that's when Ogden Police interviewed Barrios and learned that she had left her cell phone inside the car. She told police that the the child was familiar with unlocking her smart phone with the password.

Cops called it, and the toddler answered - telling them he was alone in the parked car, police said.

Police believe the suspect abandoned the child and fled on foot.

"My baby," Barrios said was her first thought. "What are they going to do to him? I don't know who it was or what they wanted. Where are they going to leave him, what are they going to do to him?"

"The mom and the officer were both speaking to the three-year-old on the phone," Scott said. "The mom was trying to console him."

Police instructed the child to lock the car doors and honk the horn, which led an officer to hear it and find the child.

The toddler was unharmed, police said.

"[He's a] very smart child, did a great job," Scott said. "[And the] mother stayed calm."

Scott says it is common for residents to leave their cars running for 20 to 30 minutes to warm their cars during winter, but warns that it's not worth leaving the car running unattended and risk getting it stolen.