Ms Clemens added: “We often lend pieces from our handling collections. They are typically used for education projects and lent out to schools.
“In this case, the gas mask was a replica of one that would have been used by civilians during the Second World War.”
The Stockton Heath Festival, which has been staged since 2008 and takes place between 3-6 July, includes 50 events from art exhibitions to live music and open-air theatre.
The children’s treasure hunt features 15 items in 15 shops in the village with World War Two being this year’s theme.