Sonny Carter, 7, was using a metal detector he got for Christmas during a walk with his parents Wednesday, the Lynn News reported. He got a hit on Roydon Common near the family's home in Gaywood, Norfolk.
The family brought the mud-caked object home and washed it off. Then Sonny's father, Jem Carter, got concerned and called a friend who had been a Royal Air Force armorer, who told him to call police.
An RAF bomb disposal team determined the bomb was a British practice weapon used on training runs. It still had its wiring in place but contained no explosives.
The family found the experience more exciting than scary.
"We are dumbfounded that he discovered this on his first go," Sonny's mother, Tracy Wood, told the News. "We are going to go out again to see if he can find something Roman. It has made our Christmas."
But Flight Lt. Donald Earl, a spokesman for RAF Wittering in Cambridgeshire, advised anyone who finds a possible bomb to leave it be and call for help.
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