It's one thing if your children are defying you to compete with one another for your attention, but it's a whole new ball of wax when they gang up on you. If you sense this is happening, be frank with any co-parent about what's going on and the need to address it as a unit.

Double Time

Create separate rewards, rules, and consequences for each child so that each child is accountable for her own actions. You can include on the list that collusion results in a “double time” reward or punishment — they can earn twice the goodies for cooperating together, or lose twice the privileges for allying against you. When you enforce this, make it swift and include both kids instead of trying to sort through facts in a who-did-what interrogation.

Divide and Conquer

“Divide and conquer” is a strategy used to take away power from an enemy by breaking up the group's unity. You can use it with your kids — any time you think they're ganging up, separate them. In the moment, send them to separate areas of the house for time outs, and confiscate cell phones if they're using them to strategize against you. Over the long term, you may need to get them involved in separate activities if these strategies don't help.