If we just focus on Britain for now (as it is all I really have any knowledge of) we can see that from the very late 19th century the levels of Child drinking went down. However, before hand it was rife. If we go back to the Early Modern Period then beer was drank by the family as a whole due to its cleanliness. In the American Colonies it was very common for the family to begin the day with a very large whiskey as Breakfast.

As we continue through and the water system improves, starting off in Liverpool in the mid-1800s, the number of people drinking decreased. However, water irrigation was still very rare in Britain, and drinking was going to carry on. A great philanthropist and quaker, Seebohm Rowntree did a social study of York and, along with finding that a large number of people lived under the poverty, also discovered that amongst these groups there was a large proportion of youth drunkenness. This level was in part cause to the poor water, the poor wages and cheapness of alcohol, and the readiness of beer and lack of regulation on who it was bought buy. There was at one time up to one public house per 500 people in London.

Forward to the 1940s and the number had dropped, Rowntree's influence and the works of other such social reformers had seen the workers wage increase and the quailty and readiness of clean, safe water increase ten fold, and the consumption of alcohol by those underage was falling rapidly.

Underage drinking was not uncommon, but it was definitely on the decline.