Q: I have two bonus daughters, ages 15 and 17. Mom has primary custody. In a conversation with mom this morning, she asked me if we were planning to buy a car for the 15-year-old. She bought a car for the 17-year-old. We were not planning on this because we pay support. I tell her this and she says she doesn’t have to provide cars for either of them and if we are not going to buy a car for the 15-year-old, then she is not going to allow the 17-year-old to drive to our house anymore. Please help me out. Do we have to buy this child a car? What is good ex-etiquette?

A: Rather than weigh in on if it’s appropriate for you to buy a car (more on that in a second), I’d rather discuss this first from an ex-etiquette perspective — and from that standpoint, it is inappropriate for mom to discuss purchasing a car for her child with you prior to her discussing it with the child’s father. Mom should first approach dad, who would then discuss it with you because you are his wife. You and dad would come to an agreement and then he, as the children’s father, would tell his children’s mother his answer.

Although it sounds like you have a pretty good relationship with mom, her going through you for an answer on any big decision, particularly financial, is a very good way to just stir things up. Plus, it sounds like this has been an unspoken bone of contention on both sides, so let the decision-makers make the decision and do your best to stay neutral — at least in mom’s (and the kid’s!) eyes.

The “well if you aren’t going to do what I want, so I’m going to” attitude is usually said out of spite and anger and breaks just about every ex-etiquette rule there is (www.bonusfamilies.com; key word: ten rules). It often backfires on the parent who says it, as well.

Co-parenting is all about negotiating in good faith and in the best interest of the kids. Rather than strong-arm your child’s other parent, look for the compromise. (Ex-etiquette rule No. 10)

First, decide if a car will even be purchased, then move on to, “Will we split the cost of the car? You pay for gas, we will pay for insurance?” But, even before that, “Will the child be required to have a part-time job to help pay for expenses?” “Will there be a grade requirement?” There are so many decisions that parents who do not live together have to make about their child driving that purchasing a car is just the tip of the iceberg!

Finally, although it is far more convenient for a teenager to have a car, it’s by no means a necessity. Food, clothing, and a place to live are necessities. It is not uncommon for divorced parents to split the cost of the extras — if at all possible.

Jann Blackstone is the author of “Ex-etiquette for Parents: Good Behavior After Divorce or Separation,” and the founder of Bonus Families, www.bonusfamilies.com. Reach her at:

drjannblackstone@gmail.com