Back in the early days, men would send their little children to a local bar to have a pail filled with beer to take home for them. Usually men who were either kicked out of the bar for being disorderly or men who were already too inebriated to go to the bar for a refill on their own. The pail of beer was so heavy that the child would "groan" and "growl" under the weight - hence the term growler. Oftentimes, the child would stop to drink some of the beer so that the pail would weigh less. If they drank too much, they'd get a good spanking when they got home.
Today, parents would get charged with child abuse if they spanked them...if they didn't spank them they would get charged with serving alcohol to a minor.