Is there a issur to kiss your wife, or show affection (not in an intimate way) in front of the kids?
There is no prohibition of showing affection to one’s wife in front of kids.
Whether it is a good idea or not, and the extent to which it should be done, is a question that different mechanchim take different approaches to.
On the one hand, it is important for children to know that parents love one another; but on the other, showing intimate affection can lead to children thinking of matters that they should not be exposed to.
If the question is affection without intimacy, I think there is no problem, and where to draw the line is a matter of personal decision.