How far should a parents responsibilities reach?

Sounds like your kids are pretty young if they're only at a playgroup. You are discovering that no matter how you bring them up, they are going to be influenced by other people - be that other children, teachers....anyone they come into contact with in fact. Yes, I think you do have a responsibility to other people's children - but this is dealt automatically by the way you behave towards them and the way your own children behave. Your children have boundaries which they know they shouldn't cross. They know right from wrong, they see from their parents' example, the way they are expected to behave. When they cross the line and swear because they've heard other kids swearing around them and getting away with it.....they KNOW that their own parents aren't going to accept that sort of language and behaviour from them. If those other children are invited to your home and they try their swearing or whatever other bad habits they've got (which they may be totally unaware of), you would tell them to stop because it's unacceptable in your home. They then learn that maybe swearing isn't what everyone else in the world happens to do just because they and their families do it. They learn by example. You can't change the world. You can't make other people's values the same as your own. You can only have your own standards which you keep to and hope that your good habits will rub off on them. Likewise, when your children become teenagers and perhaps want to do what their peers are doing, smoking, swearing etc., they may go through the phase (although never doing it in front of you unless they want to wind you up as teenagers do) - they will ultimately pass through that phase and become similar people to you and your spouse with very similar values. You can only do your best and accept that other people aren't the same as you.