I'm not a parent so I'll just state my opinion from a child's point of view, from someone who has a family thats quite similar to yours. First, how old are you children? You say they're too young to understand but if they can notice the difference in your families behavior maybe they aren't completely clueless. Now, I'm not saying they're going to right out tell you but try and watch their body language whenever you bring up the family member(s) that treated them badly or you have a problem with. I'm 17 now and when I was younger I barely commucated with my family members because they lived in different countries and I was kind of sad because of it. But, now I'm glad they were distant because I realized how twisted and selfish my family can be. All I can say is follow you gut because at the end of the end of the day your their mother and if your family wants to be wishy-washy you'll be there to tell them that it's not ok.