Obtain and read a book called "Divorce Poison" by Dr. Richard A. Warshack. It's very enlightening about how NOT to take alienating behaviors by merely "keeping the chin up".
There is specific advice related to age groups (I think - dang, I've done so much divorce related reading these days that it's all running together) and provides sample responses from the parent(s) to at least make the attempt to overcome.
In the first few chapters was a most interesting concept in that it puts a "test" on the table for when it MAY be appropriate to say something not necessarily negative, but indeed realistic, about the alienating parent's behavior. Of course, "realistic" to those of us who wouldn't consider identifying a character flaw in another means "negative" or "disparaging" to someone else. Again, it's all in the validity and delivery.
For those of us who have worked so hard to take the high road, which has usually meant swallowing a very bitter pill of silence to hear the crap that is dished out by the ex, the book's guidance and insight is a breath of fresh air.