There's a new kid on the block, and chances are he's in a stroller being pushed by a stay-at-home dad. According to the most recent U.S. Census, some 2 million men function as the primary caregivers in their families, and that number is substantially on the rise in light of the current "mancession." But what the stay-at-home dad lacks in earning power he may make up for in sexiness. There's no research on the subject, but single ladies and married moms alike seem to find stay-at-home dads hot. Are stay-at-home-dads simply sexier than their at-work counterparts? Or does their relative rarity just confer upon them a certain je ne sais quoi? "Personally I prefer a scruffy, relaxed dad to a clean-shaven, stressed-out one," says Heidi Raykeil, author of "Confessions of a Naughty Mommy." "This is why the dads at the park are often so attractive! Plus, they are engaged and active with their kids, which warms our hearts -- and other areas." Apparently, there's just something about a guy and his kid(s) that sets women aflutter. There's even research to support this phenomenon. For a 2006 study, researchers asked a group of men which photo they preferred: a picture of an adult or a picture of an infant. They then photographed the men's faces and showed them to a group of women. The results? Women found the men who liked babies more attractive, especially as potential long-term partners. "Women like to see a gentle, caring side and to know that all the work of marriage is worth it," says Raykeil. "When dads are engaged, it engages us to watch them and feel good about our choice of life partner." And this sentiment doesn't seem to be limited to heterosexual couples. "The things I find attractive in my husband of 20 years are a certain strength and ambition, a sense of humor, and now -- being fathers for seven years -- that nurturing quality that I hadn't seen before we had kids," says Dan Bucatinsky, author of "Does This Baby Make Me Look Straight? Confessions of a Gay Dad." There may be at least partly a biochemical explanation for the attractiveness of dads, and of stay-at-home dads in particular. According to biological anthropologist Helen Fisher, the latter are likely to have lower levels of the "male" sex hormone testosterone and more circulating estrogen, a "female" sex hormone. As a result, these men tend to be more interested in children, calmer, more patient, more verbally skilled, better at reading posture, gesture and tone of voice, more compassionate and more apt to have other traits necessary for parenting young children. While some women find high-testosterone men more attractive, others are drawn to guys with a softer side, says Fisher. And studies have shown that the less testosterone a man has, the less likely he is to cheat, the more supportive he is and the better he is at providing for his family. "All women want the father of their children to be interested in their kids," she says. "This makes a woman confident that he will participate in parenting and help their mutual DNA survive." And like a guy with a wedding ring, a man with a child in tow advertises "unavailability," which may make it easier for some women to find attractive what they know they can't have. I also suspect that thinking about having a man around to help care for the kids and manage household chores can help reduce stress for a lot of women. Research shows that women are more likely to experience orgasm if they feel relaxed and free of distractions, while other studies suggest that women report more relationship and sexual satisfaction when their partners help out around the house. And a stay-at-home dad can be the ultimate helper. Still, some women may find stay-at-home dads not at all sexy ... for good reason. "Even with men staying home more, women still tend to do more housework," said Raykeil. "It can be frustrating to come home after a long day of bringing home the bacon, and then have to scrape this morning bacon off the unwashed dishes." And, as with any stay-at-home partner, there's the potential for risk. A husband who stays home with the kids may start to seem dull -- or at least symbolic of the dullness that punctuates parenting sometimes, says Raykeil. "Whenever one partner is working outside the home, he or she has more opportunities to meet other interesting people that may represent excitement and exploration outside of home life," she says. Logan Levkoff, sexologist and author of "How to Get Your Wife to Have Sex With You," adds: "Our perceptions of stay-at-home dads vary based upon our understanding or acceptance of traditional gender roles. As more women enter the work force (and feel fulfilled by our out-of-home jobs), we like partners who are willing to pick up the slack. That being said, it is a double-edged sword. Sadly, if a man feels emasculated by his SAH status, it is very difficult to have a fulfilling sex life." In the end, though, parenting is about a lot more than just who, if anybody, stays home with the children. "The role of a 'dad' is changing, both in straight and gay relationships," says Bucatinsky. "People look for partners now with far more complex and varied qualities rather than just one." Raykeil agrees. "I think we're in the course of redefining masculinity and fatherhood and 'providing,' " she says. "After all, what better way to provide for your family than providing a loving and engaging relationship with your kids?" And that, everyone can agree, is sexy.