The child told administrators at My First Days Day Care he found the .25-caliber semiautomatic pistol in the grass at his apartment complex in west Toledo, the Toledo Blade reported.
Administrators spotted the gun, which the boy told authorities he thought was a cigarette lighter, as he took it from his pocket to show friends.
"We thought it was a toy, and on further investigation, we noticed it wasn't a toy and we called his parents," said Montarey Barbour, the daycare center's administrator.
When the boy boy realized the gun wasn't a toy, she said, "He was pretty upset about the situation."
About 20 children, from 6 weeks to 12 years old, were at the daycare at the time, the Blade said.
Toledo police Sgt. Joe Heffernan said the boy reportedly told his mother he about what he found, but "she failed to examine the gun."
The woman could be charged but Heffernan said that's unlikely.
"It could have been tragic," Heffernan said. "It could have been loaded. He could have pointed it at himself thinking a flame would shoot out and accidentally have shot himself."