Good cop, bad cop helpful for children's emotional development

Well, sorta.

From Science Daily:

A new University of Illinois study in the September/October issue of Child Development suggests that young children benefit when mothers and fathers differ in their reactions to their child's negative emotions.
The researchers found that when one parent provided little support in response to a child's feelings of anger or anxiety and the other parent provided a lot of support, the child had less conflict with friends and a better understanding of emotions.

It's important for parents to be supportive, but having one parent offer support and problem solving, while the other parent let the child sit with their feelings to learn to process them, seemed to let kids both build their own emotion modulation skills and maintain healthy egos.

When that happens, the child is more likely to gain experience in understanding and controlling his emotions. He may also benefit from seeing different types of reactions, realize that there are different ways of looking at things, and thus develop more complex thinking about and understanding of emotions, she said.
"We're hypothesizing that if both parents rush in to help the child, the child doesn't have a chance to experience negative feelings and learn how to manage them," she said.
The researcher emphasized that "hanging back" isn't the same as punishing a child for being upset or minimizing those feelings. The second parent should also be supportive, but quietly so, she said.

The article also talks about differences between boys and girls, and also smaller differences around whether the mother or the father plays the less supportive role.
Some of their closing conclusions:

Of the study's findings, McElwain said, "They're somewhat counterintuitive. You'd think the more support a child receives when she's upset, the better off she'd be. But the study shows that sometimes less is more."
She encourages couples to think about how they respond to a young child's anger, anxiety, or frustration as a parental unit, not as individuals. That's particularly important if a child has many negative episodes, she said.
"When you react to a negative emotion, I'd suggest that one parent step back a bit and let the other parent handle it," she said.

Makes sense to me.