It's a challenge to be a stepparent, no matter how good your intentions are. Maybe we've seen too many "wicked stepmother" stories that there is an assumption of the stepparent as being the enemy.

As soon as a new "parent" arrives in the family, the children start carving out territory. Then the adults get in on the act. Before long, the battle lines are drawn. As the kids struggle to defeat the stepparent, their biological parent is emotionally torn between kids and new spouse.

Psychotherapists have a name for it, "triangulation." Think of a triangle with three sides. That's what's happening in the classic step-parenting drama: you, your spouse and kids are triangulating on every issue. It's just constant upheaval in the home.

Kids always try to come between their parents. From toddlerhood, they instinctively know the principle of "divide and conquer". When the parents are divorced and there's a stepparent in the home, the game gets more intense.

Now the kids have a strong basis to create division, the old "blood is thicker than water" principle. And it's natural for a parent to rise to the defense of his or her child. But when that's a husband defending his child against his wife, the stepparent, it's setting up a huge conflict on two fronts - spousal and parental.

In step parenting as well as traditional parenting, the spouses must find agreement and present a united front to the children. Even if they disagree, the couple must agree to disagree in private out of ear range of the children. Never let the children know that they can divide you, because they will attack like hungry predators.

The couple must also decide who disciplines whose children. There needs to be basic rules that can be applied by parent or stepparent. Then the kids know that there's no appealing for a reprieve. Break basic rules and the consequences apply equally. That also gives the stepparent authority that the parent will back up.

Step parenting is challenging enough on a good day. The couple has to remember that strengthening and affirming their commitment to each other is the best way to create family unity. The step family is only as strong as the marriage.