YES....just ask mine...When we talk about the effect of infidelity on children, we tend to focus on the effect of divorce.
I've always noticed the effects on the children as the infidelity is active in a marriage. This is when the cheating parent is focused on the affair instead of the family, when the spouse and children become background noise (often irritating background noise), when the entire family unit is held in contempt.
Children feel this devaluing. I've never understood the claim made by both cheating and betrayed spouses that the cheater is 'a good parent.' I simply don't believe that a parent who consistently puts his/her pleasure above time spent with/attention paid to the children is a good parent. Not to mention how painful it is for a child to see the betrayed parent in such hurt and misery.
I think this all has a huge impact on children.