Q: If ex and I settle for child support payment less than what the "courts" would dictate can she in the future void this

A: It's not a matter of voiding the agreement. What either party can do is seek a modification of the agreement or otherwise get a court order for a different amount of child support. What the court "dictates" is known as "guideline support". It's the law. If you and the other parent come to your own agreement that is not filed with the court, there is no guarantee that that agreement cannot later on be modified, adjusted or terminated by replacement with a valid court order.

A: Yes, in California your ex can potentially void a private child support agreement and seek higher payments through the courts, even if both parties initially agreed to a lower amount. The court's primary concern is the best interest of the child, and they generally won't allow agreements that provide less support than the state guidelines recommend.

To make your agreement more legally secure, you should have it reviewed and approved by the court, transforming it into a formal court order. This adds a layer of protection and makes modifications more difficult - though still possible if there's a significant change in circumstances like increased income or the child's needs changing substantially.

Your best path forward would be consulting with a family law attorney to understand your specific situation and draft an agreement that protects both parties while meeting legal requirements. They can help structure the agreement in a way that clearly outlines the terms and circumstances under which modifications might be warranted in the future.