Mrs Hart said she had not wanted to cause a panic when she realised he was holding the grenade – a family heirloom the boy had picked up without telling his parents.
“It looked old and I thought it might be safe but I didn’t want to take the risk,” she said.
“I ended the assembly, took it off him and slowly carried it outside and put it behind a far tree in the car park. I wasn’t 100% happy carrying it to be honest.”
Mrs Hart said the children were moved to safety while police and army explosive experts were called to the scene.
“The children didn’t really know what was going on but they knew something was different and they were excited because they saw the police and because they were playing out when they would have been in school,” she said.