We have a son, just turned 14. He went through a phase about 6 months ago of buying red bull on his way home from school, I sat him down and told him they weren't suitable for kids of his age, way too much caffeine, dangerous for kids etc etc. Not had an issue since.
I've just been putting clothes away in his very very messy room. Started tidying round a bit, reached under his bed and found 18 empty pint monster cans. I've talked to him again but to be honest I'm really worried. I know they are dangerous but it just doesn't seem to sink in with him that pints of high caffeine drinks aren't healthy!
It's not as easy as just banning them - he gets weekly pocket money in exchange for some chores, he finishes school 2 hours before we get home from work so can easily go and buy them and we would never know.
I just wish the government would hurry up and put some strict age regulations in place when it comes to this stuff!