How do you obtain alcohol if you are underage?

in the United Kingdom you can drink from the age of 4 if you have parental permission and are in your own home

In America it depends on the state when the laws are, but most you have to be 21 to buy it. Most kids that get alcohol underage have friends older relatives or even their own parents buy if for them. But you can get ticketed and fined for underage drinking as well as the adult can go to jail for supplying to a minor, so- better think it through.