A recent research article [1] pointed out that there is a direct link between alcohol consumption and brain damage, or more specifically neurons (brain cells) being wasted. Scientists have found a direct correlation linking alcohol content in the body to neuron degeneration. The non-too surprising finding revealed that the younger a child is exposed to alcohol, the more severe the effects are on the developing brain. And this effect is very pronounced even before the child is born. So expecting mothers, please listen to your doctors when they advise you against drinking.
Although the study was based on laboratory rats, being mammals, we have to only extrapolate the results to figure out the effect of alcohol on human beings. It was mentioned that various parts of the developing brain of the rat fetus, a few days before and after birth, suffer from deleterious effects of diluted ethanol injected into the blood stream. Let's assume that a day in the life of a rat is roughly equivalent to a year for a human and you will see why a child should not be consuming alcohol before he is old enough, at least not until the brain has fully developed.
Now you know why there is a law prohibiting sales of alcohol beverages to under-aged kids. And you thought there were only social consequences. That was my impression, until I read the article. As for the effects of alcohol (read, beer and accompanying tit-bits) on adults, you don't need to be a rocket scientist to figure that one out. Just look at Homer Simpson's waistline, or the mirror. I know, I know who wants to be a 60 year old super model, right. So go ahead and indulge yourself, just don't let the kids see you doing it.