My little tip is one I read about the other week, but sadly can not recall where I saw it.
Anyway, all kids love feeding the ducks, my 2 especially.
But keeping the bread until we have enough is not quite so much fun, but now it is easy.
Keep a plastic bag in the freezer and place the scraps of bread for the ducks in there.
When you are ready to feed the ducks, take the bag from the freezer and viola, bread for the ducks that is not mouldy.