A security guard working at the Real supermarket in Wetzlar near Frankfurt, spotted the grenade on the toy aisle, and called police who evacuated the shop.
Around 50 officers searched the supermarket while experts removed the grenade for examination.
It was “most probably functional,” said a spokesman for Hessen state prosecutor. He suggested that whoever had hidden the hand grenade was intending for it to go off.
He told the Frankfurter Allgemeine Zeitung daily newspaper, “sadly we have assume he actively wanted to hurt children,” because the grenade was disguised as a toy and hidden among other toys.
Detectives are examining footage from the supermarket's security cameras in the hunt for clues, but the public prosecutor spokesman said not all aisles were covered.
He admitted they were completely in the dark about who put the grenade there, and that “the motive of the attacker is unclear.” He added that the case was being treated as attempted murder.