I know people who's grandmothers were giving them a little dram of whisky when sick etc when they were small children.
I was probably drinking at 14, if my mother of father caught me it would have been holy war in the house for a month or two. I don't think I had my first drink with parents in a pub until I was about 25, I wouldn't smoke in front of them either, such was their rage.
I'd probably have a drink with my own kids around 16, have a smoke of some weed with them too if they were interested, no coke till 18 though lol.
Seriously though, I'd rather have a drink and joint with my spawns just to talk them through it.