Brainwashing a child usually begins as frustrations, hurt, and contempt towards you by your ex. He or she feels betrayed, wronged, is quite bitter about the separation or divorce, and believes the child needs to know about these strong feelings.
Here, emotion trumps logic and good parenting. A parent makes a decision to bring the child into the separation/divorce mix, and from there the trend is rarely good—- in fact, the trend is usually towards more and more badmouthing the other parent. No matter how frustrated a parent becomes, getting the child to align against the other parent is terribly wrong. A mature parent would instead deal with the ex, and keep the child out of it.
This good parent would think, “Well, one day the child will see their parent for who he/she is, and I’m not going to be the one to slant my kid in one direction. It’s not right for me to do so, and it could even backfire one day.”
People involved in separations and divorces WILL have negative feelings towards the other parent, but it’s time for parents to act like adults and stop putting children in the crossfire. Getting a child to dislike or outright despise the other parent isn’t just wrong—it’s child abuse.