The number of men in the United States who are full-time, stay-at-home parents has risen steadily in recent decades, from maybe a million or so in 1984, according to a Pew Research Center estimate, to roughly double that in 2014.

That's still much smaller than the number of stay-at-home moms, of course, and many of the challenges these dads face are universal to parenting.

"It's a tough job," says Ben Sanders, who's raising two young boys in Haymarket, Va. His kids are 3 ½ and 6 ½ years old. "There are no breaks. It's 24/7. There's no vacation. You can't get sick."

The amount of work entailed "is crazy," Sanders says. "You're on your feet constantly, you know — shopping, laundry, errands [and] running kids here and there. It's very hands-on. It's very demanding. I've lost over 50 pounds, just being a stay-at-home parent."

And adding to the crazy stress of child rearing, he says, there's this: Some people still aren't comfortable with a man being the caregiver full-time.

Lining up play dates for his kids, for example, can be awkward. Initially Sanders signed up for a mom's group in his neighborhood, but didn't feel completely welcome there. He tries to shrug it off.

"It's like being in sales," says Sanders, who used to work as a regional sales manager for a solar energy company. "People say 'no' all the time. If you're in sales you can't have a fear of rejection, you know? You ask enough stay-at-home moms if they want to have a play date, and maybe one or two out of 10 will says 'Yeah, let's do it.' "

Researchers who study stay-at-home parents say that difficulty in making social connections seems to be one of the biggest obstacles dads face. In many parts of the country there are so few men doing this that they have a tough time finding each other.

Reaching out to nearby moms isn't always an option; stay-at-home moms often feel more comfortable hanging out with other women. And some working fathers frown on other men socializing with their wives when they're away.

"There are people who don't understand," Sanders says.

His wife, Nicole, who has a high-pressure job with a large defense contractor near Washington, D.C., is grateful to her husband.

"I don't think I could do my job if he weren't at home," she says. "I travel a lot. My schedule is very erratic and unpredictable."

Knowing that there is always someone covering the homefront allows her to be very flexible in her work hours, she says. "And that's kind of the nature of what I do."

After their first child was born, the Sanders both continued to work full time. Ben was on the road Monday through Thursday, and the couple hired a pair of nannies, who worked in shifts to help bridge the gaps. "They switched off every 12 hours," Ben says.

But he says that pace was too hectic for the family; Ben and Nicole finally decided one of them needed to stay home full-time.

Ben was ready for a change and no longer wanted to feel like a weekend father.

"I wanted to see my family every day," he says. "I actually wanted to be part of my children's life and be present — not absent. So that's what we did. And there's no looking back."

U.S. census data from the early 1970s show very few men listing their occupation as "full-time parent." So, how about today, after four decades of struggle for gender quality?

"It's still relatively uncommon," says Brad Harrington the executive director of the Boston College Center for Work and Family. "Depending on whose numbers you believe, it's somewhere between 1 out of 20 or maybe one out of 15 at-home parents now is a dad."

In his own research, Harrington has found that more than half of male millennials say they would consider being a stay-at-home dad if their spouse earned enough to support them. Yet he's found a disconnect, he says, between what people say they mightdo and what actually happens.

Partly, he says, that's because of continued income inequality between men and women.

"Oftentimes the financial decision goes in favor of the woman staying home rather than the man," he says.

And corporate culture, he says, particularly at large, established companies, can still discourage fathers from taking years off to be home with their kids.

"There is kind of a lag between the experience of young fathers these days," Harrington says, "and what the people at the top expect from young working dads."

Those corporate expectations of dads can be incredibly harmful to mothers, as well as to the fathers, Harrington says.

"Nothing, probably, provides more of an opportunity for women to advance than an at-home dad," says Harrington. "Because when they know that the father is there, taking care of that set of responsibilities, then women are more free to pursue their own professional goals."

On a Wednesday morning in Arlington, Va., a dozen stay-at-home fathers and about 20 kids get together for their weekly dads' group. The kids range in age from a few months to 9 years old. Some of the older kids are playing dress-up in the basement. Another boy is building a Lego tower in the sunroom.

Dads are drinking coffee, eating doughnuts and hanging out. Just as women have found comaraderie in "Mommy and Me" groups, these fathers enjoy their own social events.

Mark Bildner, who serves as host this day, is a veteran of the local D.C. Metro dads' network. He's raising four kids; the eldest is 10. Bildner says he finds that men often have trouble breaking out of the work mindset and getting into the world of parenting. At work, he explains, projects tend to be linear — the goal is to finish one task and move forward to the next, then hit the next goal, the next milestone.

But parenting isn't linear, Bildner says. It's more like the ocean.

"The tide comes in, the tide goes out. The house is clean, then it's dirty. Your child is happy, now she's sad. She's tired, now she's rested."

Bildner gestures at the kids scampering around his carpeted basement. "An hour ago, this room was completely clean," he says. "Now it's wrecked."

As a parent, Bildner says, you have to have a different vision of progress. "You just have to accept that things get done and undone all the time. Your job is to just go with that," he says.

Accepting the ebb and flow of a child's world can be hard for a man who expects something he's fixed to stay fixed.

One of the fathers in Bildner's basement, Aaron Rosenbaum, calls this group "fantastic" and says it fills a void for him and his friends.

"It's just the camaraderie," he says. "No one feels uncomfortable around you. You don't feel like people are wondering why you're staying at home."

Rosenbaum used to live on Capitol Hill in D.C., where he says there were "tons" of activities for young kids.

"But I was almost always the only dad," he says. "Most moms seemed completely fine with me being there, but lots of times I felt like a lot of people wouldn't actually talk to me, or just kind of avoided me. So in some respects it was a little lonely."

Parenting, of course, can also be a lonely endeavor for a stay-at-home mom who suddenly finds her world swirling around a nonverbal infant.

But Rosenbaum says the fathers he knows aren't as good at overcoming that social isolation.

"I feel like moms are more likely to come out of the woodwork and get together and do stuff — make sure their kids play together," he says. "Dads tend to be kind of loners."

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