We have simply told the younger generation, including children and young neighbours, my nieces etc. that they are more than welcome to ASK for advice or help if and when they need it, but that DH and I have absolutely no intention of offering advice, that is neither needed , wanted or has been asked for.
However, in our home, we have once or twice told a child firmly and kindly in a quiet tone of voice, that we do not do (or say) that in our house. One grandchild did come back with "but Dad lets me at home" to which I replied "what Dad lets you do at home is no business of mine and I am sure he will tell you that what we say the rules are here, is no business of his"
A phone call to Dad made by my indignant GS resulted in the young man being told exactly what I had just said.
Bringing up children is bound to differ from one generation to another because we are living in a different society now to the one we brought our children up in and there is always a certain amount of peer pressure from other families.