I'm not sure I agree with this 'introduce them to alcohol slowly so they get used to it' stuff.
I was never given alcohol as a child, never wanted any. I'm the oldest of 4 siblings. We all have very little interest in alcohol as adults, so I don't see how not giving us alcohol would have any bearing on us binge drinking. None of us did that as teens either.
I've been drunk about 5 times as an adult and the last time was about 15 years ago. I have a bottle of wine in my fridge now that was given to me as a housewarming present 4 months ago. I've had one glass and didn't really enjoy it.
My own dc (well, the older two) have had sips of wine/lager/Guinness at various times, to see what it was like, and declared them all horrible. Other than that they aren't interested. Youngest is 5 and the thought of giving him a glass (whatever size) of any kind of alcohol, regardless of occasion just seems weird - he's a child, he's happy with squash, alcohol is for adults - he doesn't need or want it.
Maybe this will change as they get older, but I don't feel the need to acclimatize (for want of a better word) them to alcohol and I honestly don't understand that attitude - it seems really alien to me.
BUT. If other people want to give their children the occasional snifter of something, fair do's. As long as they're not falling down pissed, meh.