Many things can make child custody situations more difficult than they have to be. One of these is when you have a co-parent who is uncooperative. Part of the basis of this type of parenting arrangement is that both parents work together for the good of the children. When this doesn't happen, you might have to reevaluate the style of parenting you're using for the children.
One of the most important things to remember when you're in this position is that the only thing that matters is how the children are faring. There might be times that you and your ex have to agree to disagree. Taking a step back in these cases may help you to put things into perspective.
Are the children happy, healthy and safe?
The goal of the child custody situation is that the kids should be happy, healthy and safe. If you and your ex aren't agreeing on specific terms of the arrangement, you should reflect on whether those three points apply to your children. The disagreement could come down to personal preferences that don't really have a direct impact on the children. Ideally, you'll save your energy for battles that negatively impact the child's happiness, health or safety.
How does the situation affect your home?
The decisions your ex makes shouldn't directly impact what you do at your home unless you agree to them. If they are changing things at their place, you may have to accept the differences between the homes. Children are fairly resilient and will probably be able to adjust to the smaller changes. Speaking up about the things your ex changes at their home is really only appropriate if they directly violate the parenting plan or if things are having a negative impact on the children.
Does the situation warrant a parenting plan modification?
The issue that may cause problems between you and your ex could be because the current parenting plan doesn't address the child's needs any longer. If this is the case, you might consider working out a modification of the plan. This could help you to ensure that the guidelines you're following are what your child needs right now.
Remember, your child's best interests must always remain at the heart of child custody decisions. If you and your ex can't come to terms on major points related to the children, you may need to turn to the court system to make those decisions for you.