I'm not sure where you got this information, but I'd be interested to see a source. As far as I know in the middle ages beers and ales were brewed using the same mash multiple times leading to varying strengths ranging from 10-12% for the first batch to very little alcohol ~1% from the third batch. And of course there were also various types of wines available. Children drank only the weak beer, but there was definitely high alcohol content drinks available.