If U.S. birth rates — declining steadily since 2007 — stay at their current level, the average woman is expected to give birth to exactly 1.9 children in her lifetime. And until we figure out how to raise 90 percent of a child, we're going to focus on that first number: 1.

Only children are far from an anomaly: 15 million households had exactly one child in 2011, according to the U.S. Census Bureau. Single-child families, in fact, have been equaling or outnumbering two-child families for most of the 2000s, according to federal Current Population Survey statistics.

But they do present a set of parenting circumstances that is altogether different from the challenges of raising two or more children.

"One family size is not better than another," says social psychologist Susan Newman, author of "The Case for the Only Child: Your Essential Guide" (HCI). "Just like having a set of twins is different than having four children, how you approach raising one child is different than how you approach raising more than one."

As more families hold steady at one child, Newman says it's important, first and foremost, to let go of stubborn, misguided stereotypes of onlies as lonely or socially maladjusted — ideas that have been disproved by study after study for more than 30 years. Especially, she says, because the stereotypes took root in the late 19th century, when child-rearing looked quite different from today.

Harvard psychologist G. Stanley Hall set only children on a long and stigma-filled path when he released a study in 1896 that declared, "Being an only child is a disease in itself." (He was also a strong proponent of selective breeding and forced sterilization, but that's neither here nor there.)

Newman has spent the last few decades researching onlies, a topic she touches on frequently in her "Psychology Today" blog and her 2001 book, "Parenting an Only Child" (Doubleday/Broadway).

"Children no longer live isolated on farms," Newman says. "Today we have day care and nursery school and after-school activities that don't end until 7 o'clock at night. It's during these activities that only children learn sharing and caring and empathy, and how to interact with others and stand up for themselves in much the same ways they would if they had siblings."

Still, what happens (or doesn't happen) at home profoundly affects the way children go through the world, which is why experts advise parents of onlies to tailor their style accordingly.

Play your way. "Let your child know that other people get a say," Newman says. "If your child always wants to play Candyland, tell him, 'I'll play a game with you, but I feel like playing Chutes and Ladders.' Encourage attention-giving in your child, so he learns to pay attention to others and what they want."

Raise a groupie. "Encourage team sports and group activities like band," Newman says. "Unless you have a child who is an extremely talented pianist or an ace tennis player, seek mostly group activities."

Send them away. As your child gets older, find ways for him or her to join those teams or groups on overnight getaways. "You want them to go away on retreats and sleep-away camps," says child psychologist Jennifer Powell-Lunder. "It teaches them how to live with their peers and ultimately prepares them for when they go away to college."

Think big. "With one child, it's very simple to pick up their dishes from the table and put them in the dishwasher and pick up their laundry and do their homework with them," Newman says. "But your child needs responsibilities. Before you do something for your child, ask yourself, 'Would I be doing this if I had two or three or four kids?' Because you're doing your child a disservice if you don't let him have any responsibilities."

Step aside. "Parents can become very enmeshed in the friend, confidant role with an only child," Powell-Lunder says. "It can be helpful to encourage a relationship with other adults around you — a favorite aunt or some other adult they can turn to as support so they're not taking all their cues from you."

When it comes time to talk puberty and dating and other sensitive topics, don't feel discouraged if your child seeks someone else's input — just as a child might turn to an older sibling for advice. "Sometimes only children even will go to their best friend's mom, and that's OK," says Powell-Lunder, who co-wrote "Teenage as a Second Language: A Parent's Guide to Becoming Bilingual" (Adams Media).

Leave them alone. One benefit of living without siblings is … living without siblings. Don't feel like you have to fill the space. "Many parents of only children worry about how much time their children spend alone," Newman says. "You should absolutely not worry about that. We're all alone at some point in our lives and time alone teaches the child how to be happy and productive by himself; it encourages creativity and finding positive ways to fill your time."

Plan ahead. "Encourage your child's social life from early on because some of those friendships will become lifelong and prove critical in terms of support — in addition to your child's partner or spouse," Newman says. "Research shows the two main reasons parents strongly consider having a second child are to give the child a playmate and so there will be more people to take care of (the parents) when they age. They fantasize that their offspring are going to rally around their bedside taking turns." (In reality, Newman says, one sibling tends to take on the majority of the care for aging parents. And siblings aren't guaranteed to get along in adulthood any more than childhood.)

Surround your only child with as many friends, cousins and close-in-age relatives as you can, Powell-Lunder says, and he or she is likely to reap the same benefits into adulthood as a child with siblings.

Fact vs. fiction

Social psychologist Susan Newman tackles some common myths about only children in her books, "The Case for the Only Child: Your Essential Guide" and "Parenting an Only Child: The Joys and Challenges of Raising Your One and Only," portions of which are adapted below.

Myth: Only children are aggressive and bossy.

Fact: Only children learn quickly that attempting to run the show doesn't work with friends, and a bossy, aggressive attitude is a quick ticket to ostracism from the group. Lacking siblings, only children want to be included and well-liked.

Myth: Only children are spoiled.

Fact: Researchers have found that only children are not particularly spoiled and found no difference in only children's relationships with friends when studied with children who had siblings.