Should have also said that my kids are 6 and almost 13. I don't have any issue with people drinking when their kids are there as long as they aren't getting blotto, I don't think seeing your parents being a bit merry, having a good time and laughing more than usual is harmful really. But getting very drunk (can't talk without slurring, can't walk straight etc) can be pretty scary for children to witness.
An old uni friend of mine regularly gets absolutely smashed in front of his daughters. He's one of those 'life and soul' types and is hilarious, but I'm not entirely convinced when he claims that his kids just laugh and roll their eyes at him as 'they know what I'm like, they aren't bothered, they think it's funny'. Maybe now they are in their late teens they're not as fussed, but when they were small it can't have been fun having him plastered in sole charge every weekend.