Sweden's national bomb squad were called to a preschool after a child brought a live grenade into class, sparking panic.
The incident, which occurred in Kristianstad in southern Sweden, ended with the bomb squad neutralising the device but the officer in charge said it "could have gone really badly".
Staff called police after finding the device in the evening, after children had left for the day.
Police then identified it as a grenade and called the bomb squad, who assessed the grenade as too dangerous to move and dismantled it at the scene.
A spokesperson told CNN that a child found it at a nearby military training ground: "The military uses these big open fields for exercises, but at certain times of year they are open to the public when there's no shooting going on and people are told not to touch anything out of the ordinary."
Thomas Söderberg, the officer in charge at the scene, told the Expressen newspaper that the event could have had a very different ending.
He said: "These are extremely dangerous things. If it had exploded when the children were around it, it could have gone really badly."
"The child in question probably thought it looked cool and wanted to show it off. As I understand it, the parents didn't know that they had the grenade at home."
The case follows a similar incident in Sweden weeks ago, when a primary school pupil brought a live grenade to class and placed it on a ping-pong table.
A member of staff came in and almost had a heart attack," said Söderberg, who noted that device in that case was found to be inactive.
"What happened is not good and I assume the parents will have a little conversation with the child."