My reading of nineteenth-century American literature and periodicals 
has taught me two things. If there was a law, it could be widely 
ignored. America was not much of a police state, especially before the 
Civil War, and the decision to serve minors or not serve minors would 
be something that the tavernkeeper would often make under no or some or 
great scrutiny from his immediate community (and constituency and/or 
customer base).

It also appears to me that children were often sent to fetch alcoholic 
drinks for their parents. A child who makes regular runs to a bar-room 
or pharmacy to purchase something for his parents would have no trouble 
purchasing the same for his own use. There's no doubt, for me, that 
some lazy parents would resist the enforcement of a minimum purchase 
age on this count alone: it would mean that they would have to go get 
their own buckets of beer or quarts of Lydia Pinkham.

Jon Miller