Waseca police are reassuring parents that three tiny explosive devices found on a school playground have not posed a hazard to the public and that it's safe for kids to return to school Monday.

Two very small homemade devices and a damaged stuffed toy containing a third device were found last week on the south end of the playground at Hartley Elementary School, police said Friday.

Responding to phone calls from worried parents and increasing public concern, police Saturday released additional information, updating the description of the discarded devices. They were small, compressed-air cartridges similar to those used in a BB gun or pellet gun, police said.

The devices appeared old. Two had been detonated previously, and a third had failed to detonate, police said. They required an open flame to ignite.

The condition of the devices indicated that they were likely left there for weeks or months, then found when snow melted.

Police on Friday had withheld descriptions of the devices as they investigated, but then sought Saturday to assuage worried parents by releasing a more detailed description.

Waseca police ask that anyone with information on the devices call them at 507-935-9720.