I don't think you validate her saying the kids will be better off. We all know that isn't true. Whatever else she says, maybe validate. But not that. If you validate that, it gives her a clean concious about doing it to the kids. I personally didn't and still won't. Maybe you are better off saying nothing when she says that. But don't agree with her on that. And don't feel bad for standing up for your kids on that issue.
Validating doesn't mean you agree but that you understand the other persons POV. "I understand that you think/feel ___________." You are acknowledging their feelings and thoughts, shows you are listening and that you are considering them.
Ex. "Kevin, I understand how you feel about standing for your marriage."
M22,H45,W45 S21/18D12 Retain faith that you will prevail in the end, regardless of the difficulties and at the same time confront the most brutal facts of your current reality, whatever they might be.