Remember that your kid is a fellow human being. Yes you brought him/her into this world. But they are still a separate human being, with their own ideas, thoughts, dreams, fears, feelings, and life. Look at them as such. See them for who they really are.
Don't Over-Compensate for the Narcissistic Parent
When our co-parent is abusing our children in any way, it is extremely easy to over-compensate by trying to erase all the bad feelings in our child. Our intentions are good. We know that those bad feelings are coming from the way they are being treated. So if we can erase those bad feelings, then maybe we can erase the damage they are suffering. However the results may not be quite what we hope for.
How to Turn the Table on a Narcissist
Narcissists absolutely hate for the other person to be right. Especially if that person is a spouse, significant other, parent or child. Use their own desire to always be right and to always prove you wrong against them. Anticipate their irrational reactions before they happen and call them out on it ahead of time.