Tiny Dancer

I hear a more fundamental problem to what you have described: You and your ex-wife have different values, principles or expectations for life (...and parenting) right now. While providing a healthy and balanced life for your son and daughter is important (we'll get to that a bit later), I think there are more significant issues at play here and the issues with your son and wife are simply a manifestation. Basically, you've described a symptom of a bigger problem. Before significant change can occur, I believe you and your ex-wife need to discuss (with the help of a neutral third party) what your individual values/principles are and how to co-exist and co-parent with these different and maybe competing values. Scary stuff but essential. I would not be surprised if this takes several months of work to figure out the following 'equation' - Values > Thoughts > Behavior > Parenting. Bit over-simplistic but you get the picture.

Now, in the meantime since that values work will take awhile to get going and get some traction, let's talk about how you can intervene in the current mess. Here are some quick steps you can take starting today to support your son and be a fantastic parent:

1. Resiliency: Help your son develop greater resiliency to ANYONE that does not support him or fails to give him what he needs. In car rides back home, on the way to school and during breakfast, talk with him about times you did not get your needs met and how you overcame it. Share with him how you handle difficult situations (DO NOT use your ex-wife in these examples). Ask him what he thinks would be a good and effective strategy to cope with those that treat him poorly. Remind him often of those that do love and support him and encourage him to share is good and bad experiences with them. 

2. Internal Locus of Control: Teach and role model personal responsibility for one's thoughts, feelings and behavior. Talk with your son and daughter about how we all have choices about what we control. I use the analogy of a hula-hoop - everything inside of your hula-hoop is yours. The good stuff you do, the good thoughts you have and the good feelings. This also means that your poor choices/behaviors are also yours along with your bad thoughts and feelings. Blaming others for how we feel, what we think and how we act is ineffective, dishonest and does not accomplish anything expect perpetuating problems. Another by-product of teaching/role modeling internal locus of control is your son will develop very healthy boundaries for himself and others. Kids with this role modeling develop healthier relationships and are way less likely to be victimized in relationships or random acts. They are also the ones that will often stand up for others if someone else is being abused. Who doesn't want a kid to grow up to be like that?

3. Don't Attempt to Rebalance: Things are not equal right now and that's just how it is. No need to over compensate with buying your son toys or food or going above and beyond to give him more experiences. Go with the flow, be a great role model, offer support and teach healthy boundaries. Teach him what it means to be a young man and live well in an imperfect world. Your ex-wife is not the last person that will treat him unfairly. Will you really trying and counterbalance all future injustices that he faces? Probably not. 

4. Play Therapy: Finally, taking him to a certified play therapist would be a great way to provide him with a neutral third party to whom he can express his thoughts and feelings. Play therapy is not playing with toys and getting a big fat therapy bill. It's a very complicated process that requires significant training. Play in play therapy is simply the medium or vehicle for allowing children to provide a safe experience during which they become more relaxed and often are able to explore sharing thoughts and feelings more easily. Wouldn't be bad to invite your daughter to attend with your son occasionally so it's normalized that both of them are going. Lastly - if there is anyway your ex-wife would go, invite her (or better yet, have your son invite her) to participate with him in play therapy. It's amazing how this environment can really bring out a more compassionate side in even hardened parents. 

Ok, Dad. You've got your instructions, now go and make it happen. It's clear you are a thoughtful, caring father that will do great things with your son. Best of luck in such a complicated situation.