To me 'fighting' means raised voices, nastiness, etc. And I don't think that is ok in front of kids. I don't think there's any question that that will have an effect on them. I have seen poor DD's face before when she has thought we were fighting, when DH has chased me and I have screamed or yelled. We were just playing and he was trying to tickle me but she obviously thought we were fighting or something and burst into tears. Of course there will be times when this does happen in most houses occasionally and then I think, like others have said, it's important to explain and let them see you make up.

'Arguing' I think is ok. I think it's good for them to see you are both individuals with different ideas/beliefs and that you can resolve an argument and move on!