(ThyBlackMan.com) Much of the time one parent does not realize what they are doing. The effect on the kids is unnoticed. It is usually experienced by the child as stress, tension, anxiety, guilt and depression. Kids may act out or hide it. Parents usually justify it.
What is “it?” On the moderate side it is undermining the other parent and it can lead to alienation. While some parents undermine themselves, one parent undermines the other when intentionally or non-intentionally one parent sends a message that a positive relationship with the other parent is not that important.
How does this happen? It may happen not so much by what a parent says but how he or she feels when he or she says it. One may be concerned about his or her child’s welfare when questioning the child about the other parent, but the child may perceive your concern as if the child is in a bad situation. 
Subsequent comments may suggest to the child that something is bad about the other parent. Perhaps the comments are an exaggeration of the other parent’s flaws. A parent’s natural wish to protect a child may lead to proposing ways the child can deal with this “awful” situation, and maybe even question the appropriateness of time spent with the parent.
The next step in undermining the parental relationship would be to give power to the child in deciding whether or not a parental relationship is appropriate. While most parents would not hesitate to insist their child do something that they must do, building a workable relationship with the other parent may be seen as optional. For a child, though, to choose between having a relationship with a parent and not having a relationship is distressing. Even though kids may complain about their parents and protest against seeing a parent, they generally deep down want a good relationship with both parents. When one parent sides with the protest, however, the child may see this is a way to connect with the “better” parent, and the other parent may lose out.
The more the child avoids the “problematic” parent the easier it gets to avoid the “problematic” parent. Plus, the child gets approval and attention from the “better” parent. A powerful reinforced cycle develops.
The child may react by idealizing one parent and devaluing the other. Or the child’s complaints are listed and some of them are trivial or untrue. The complaints sound like they don’t reflect the child’s true feelings, or there is little ambivalence. Children may deny hope for reconciliation.
Children who are burdened by an undermining parent learn that it is not possible to have a good relationship with both parents. The other parent may give the child space to come around, but this may inadvertently reinforce negative perceptions. Or, the other parent may “push” the relationship, again reinforcing negative perceptions. Also, the parent may respond to undermining by undermining the other parent, and then underrate the effect on the kids. Both parents end up with little insight into one’s own contribution to the problem.
The effect on the kids can include changes in how the child views the world, lowered self-esteem, loss of self-confidence, future conflict, issues with attention, depression, and/or anxiety, future addiction and other effects revealed by research. Unfortunately, kids identify with negative aspects of both parents. Often though, the better the relationship with one parent the better the relationship with the other parent.
Written By Dan Blair
Official website; http://blaircounselingandmediation.com/
