I went on a couple of websites where dads are fed up with moms, especially in Canada. The dads stated that the mothers were bad mouthing them, and they felt like the children no longer wanted to be a part of their lives. They also felt like the courts always ruled in favor of the mothers even when the mothers were in the wrong.
When one parent makes derogatory remarks to the child about the other parent, the child may not want to see or talk to the alienated parent. This called Parental Alienation Syndrome.