Actually, before the
fifteenth century beer was brewed without hops, and so was brewed often. Everyone drank very
strong beer with their meals, and even the
children drank beer. However, the children weren't given the same beer as the adults, but instead had a 'small beer', which was less
alcoholic - Which is where the saying comes from, similar to
child's play.
The irony is of course, that even the small beer consumed by the kids was more alcoholic than full strength (around 5%) beer today.