Fighting parents can have life-long lasting effects on their child's ability to trust in both romantic and platonic relationships. If you believe your ex-spouse is exposing your child to negative opinions about you, it's important not to stand by.
Talk it out
The first step is to have a discussion with your ex-spouse in the most respectful way possible. Try not to place blame on your ex or say anything that might antagonize them. This will likely fuel the fire.
To ensure that the conversation is peaceful, you may even consider bringing in a third-party to mediate the discussion. Using a child psychologist as a mediator is one way that the two of you may be able to reconcile your differences in the best interests of your child.
Explain that you don't want to damage your child's perception of each parent as a role model. Doing this can make it difficult for the child to trust either parent as well as others in future relationships.
Try co-parenting classes
Another way to work through your differences with your ex-spouse could be to attend co-parenting classes. These classes train divorced or separated parents to keep their child's best interests at the forefront of all of their decision making.
Seek legal action
If you have tried to reason with your ex respectfully and still aren't getting any results, you may need to resort to legal action. It's important to preserve a positive relationship with your child and to keep them from feeling as though they need to choose a side.
A Family Law attorney can help you assess your situation and advise whether a change to the custody order is necessary.