Why did children in World War 2 have to have a tin with cotton wool and a cork?

My understanding is that children were given these in the event of a bombing of their location. The Cotton Wool was, of course, to put in their ears for 'protection' while the cork was to be bitten on in an effort to stop children biting their tongue.

Whether either were effective would be another question, but it was certainly providing the view that something was being done for the 'protection' of the children.