A group of Oregon children came across an undetonated, World War II-era mortar shell at the Oaks Bottom Wildlife Refuge and brought the military explosive to a play date, Portland police said on Wednesday, The Huffington Post reported.

The foot-long mortar shell was probably discarded in the park and authorities do not expect to find any more live bombs in the area, according to Portland Police Bureau spokesman Pete Simpson.

Police received a call on Tuesday saying that some kids had brought an un-detonated explosive they found at the wildlife refuge to a residence in southeast Portland. Once officers learned that the mortar shell had been moved to the home, they brought in explosives experts to remove the mortar shell and started evacuating the neighborhood as a precautionary measure, according to The Oregonian.

"It's a mortar shell and very old," Portland Police Bureau spokesman Pete Simpson said. "Not clear how old, but certainly decades, at least."

Sgt. Jeffrey Sadler, an explosive ordnance disposal technician with the Oregon Air National Guard's 142nd Fighter Wing, identified the explosive as a 60mm illumination mortar shell, "typically used during night operations to illuminate parts of the battlefield to help identify enemy force."

Even though the mortar shell is decades old and rusty, Sadler said it could be extremely dangerous.

"Over time, many of the mechanical safeties can wear down and deteriorate, making fusing systems very unpredictable and dangerous," he said. "Explosives themselves can also be unpredictable. Some become more hazardous with age while others decompose and lose their explosive properties," The Oregonian reported.