I think issues with a friend's kids is probably the second biggest killer of a friendship behind issues with the partner your friend chooses.

I do think kids should behave well when out, and certainly when in someone else's home. Mine do, but that's because I jump on them if they don't and they know it. They are allowed a much freer rein at home or my mum's.

If there are children in my home who are doing something I'm not happy with and their parent isn't doing anything about it then I say something gently, and hopefully the parent takes it from there if further follow up is necessary. If they don't then I do. Its my home so to a certain extent my rules.
I'm the same as Lulu.

Unfortunately all parents expectations of how their children should 'behave' is really different. Some are made to sit quietly, others can run around crazily etc.... I know I expect my DD to behave (as in don't play in kids bedrooms, jump on furniture, use a quieter voice when inside etc...) but does that mean she always does? No! But like Lulu, I am on to her if I see her doing something I don't think is acceptable & if I see someone elses kids doing something unacceptable I will step in if the parent isn't around or watching.