Theo and Benoit Donaldson, 13, found a grenade using a metal detector in a park in east London.
They dug down about one foot and recovered a WWII Mills bomb. From there, they showed it to their mother Marie Donaldson, 46, who told them to take it home so they could look it up online. At first, they thought it was a giant acorn.
On the way home, they threw it between each other, dropping it several times.
They did not realize what it was until their uncle, a policeman, saw a photo of the grenade their mother emailed to him.
He alerted the area bomb squad, who removed and destroyed it.
“It was a big bang. That’s when the shock really set in,” said Marie Donaldson.