Who Can Kill a Child? (aka (Island of the Damned), Trapped)

An English tourist couple rent a boat to visit the island of Almanzora, just off the southern Spanish coast. When they arrive, they find the island apparently empty of adults. There are only children, who don't speak but just stare at the strangers with eerie smiles on their faces. The English couple soon discovers that all the island's children have been possessed by a mysterious force, a kind of madness which they can pass from one to another, and which makes them attack and murder their elders, who can't defend themselves because, of course, nobody can kill a child