To me, NC with small children should only be done if the MLCer is either ignoring the children or is Monstering at them, like Chriss's H. Then it is to protect the kids.
If the MLCer is still trying to parent, and spend time with their kids (which isn't that often), then NC would only hurt the kids.
Even if the spouse can't get along with them the children should have a chance to have both parents in their life. Even divorced parents can still parent.
So I think it all depends on how the MLCer is acting towards the kids. Do they want to be involved or not?
Are they treating their kids well or not?
If they Monster at everyone..NC for sure!