In 1968, only 20 percent of mothers with a child under age 5 were in the work force, according to the U.S. Department of Labor. By 2002, that number had reached nearly 60 percent, and by 2011, nearly 64 percent.

The shift has been especially profound among white women, researchers say — and has led to fathers spending more time caring for their kids than ever before. In fact, fathers have nearly tripled the amount of time they dedicate to child care from 1965 to 2011, according to a 2013 report from the Pew Research Center. They now report spending 7 percent of their time on child care — compared with 2.5 percent in 1965.

Mothers, while still devoting more of their time to taking care of children than fathers, also reported an increase in the time they spend on child care, from 10 percent in 1965 to 14 percent in 2011.

"Fathers have gone from being occasional assistant parents to being much more active co-parents," says Michael Lamb, PhD, a Cambridge University psychology professor.

This gender convergence in the way mothers and fathers divide their time between work and home is good for families, says Ross Parke, PhD, a psychology professor at the University of California, Riverside, and author of "Future Families" (Wiley-Blackwell, 2013). Decades of research by Parke and others suggest that parental roles are to some extent interchangeable — that fathers and mothers both can serve as competent caregivers and provide the critical ingredients for children's optimal development.

And while, traditionally, mothers' and fathers' styles of interacting with babies and toddlers have differed, with mothers providing more gentle and verbal interactions and fathers engaging in more physical, rough-and-tumble play, children develop into capable social and intellectual individuals in families in which parental roles are reversed and shared equally, he says.

"We're in a period of flux, where you can almost think of parenting as kind of a cafeteria model, with various components that need to be included, such as nurturance, sensitivity, educational guidance, stimulation," Parke says. "Historically and culturally, this was often a function of gender, but it could be as the roles change and we move away from the two-parent, picket fence 1950s family, parents can choose the components they're most comfortable with providing. The research is showing it won't do the kids any harm."

Evidence also suggests that mothers and fathers are providing similar levels of support and advice to children into young adulthood. In a 2012 study, for example, researchers led by Karen Fingerman, PhD, a psychology professor at the University of Texas at Austin, surveyed 633 middle-aged mothers and fathers about how often they provided emotional, financial and practical support and advice to their adult children. They found no difference in the amount of support fathers provided compared with mothers, and no difference in the amount of support needed by sons or daughters. Fingerman says she has seen similar findings in several recent studies related to rates of parent-child contacts and strength of parent-child ties among this cohort.

"Mothers are still more involved — both emotionally and on a day-to-day basis — but not consistently and not as much as they were in older generations," Fingerman says. "That's not necessarily because mothers are less involved. It's likely because fathers are more involved. Some fathers who are divorced or never married the mother may not have a relationship with their grown children. But the involved fathers are looking a lot more like mothers, which is a great finding because it means we're seeing more family cohesion, even after the kids are grown."

Amy Novotney is a journalist in Chicago.