The trail of bread crumbs didn't work. It was the pebbles that worked. The smooth polished pebbles that gleamed in the moonlight. But then they got taken out again before the pebble supply could be restocked and used bread crumbs as a substitute which failed because the birds came and ate the bread crumbs.
Which is why you shouldn't feed the pigeons: it encourages them to help witches eat small children.