Your baby's general outlook on life depends at least in part on when she joins your family. "If she's your firstborn, she has greater odds of being a high-achieving leader, such as an airline pilot, a principal, or a business owner," says Dr. Leman. And -- don't tell her younger siblings someday -- oldest kids tend to be slightly smarter as well. A Norwegian study that looked at nearly 250,000 18- and 19-year-old men found that on average those who were oldest children had an IQ three points higher than that of the next oldest sibling and four points higher than the one after that.
One big reason? You. "The oldest child gets his parents all to himself for a period of time," points out Joseph Price, Ph.D., professor of economics at Brigham Young University, in Provo, Utah. According to his research, firstborn children between ages 4 and 13 spend 3,000 more hours with their parents -- roughly an hour a day -- than each subsequent sibling does. That's because parents have to spread themselves thinner once they have two or more kids. So even if you're always around the baby, he may spend a significant chunk of that time sitting in a bouncy seat rather than sitting in your lap listening to a story.
While younger sibs may get less one-on-one time with you, they benefit in other ways. "By the time a second child comes along, you've probably become a better parent, and an older sibling often helps out by teaching a little brother or sister what he knows," says Dr. Price. Because he needs to compete for your attention, the youngest child in the family tends to be more outgoing, often developing "Look at me" skills and a class-clown personality (a long list of comedians, including Steve Carell, Jon Stewart, and Ellen DeGeneres, are the baby of their family).
Middle children often become masters of negotiation and compromise -- so they can keep the peace between their older and younger siblings and earn their busy parents' approval. And only children, who tend to spend a disproportionate amount of time in the company of adults, are usually more reliable and mature than typical kids, notes Dr. Leman. Despite the "only lonely" stereotype, growing up without live-in playmates doesn't seem to hurt their social skills any. A recent Ohio State University study of more than 13,000 teens and tweens found that singletons were just as popular as those who had siblings.
What you can do now: Make a concerted effort to spend as much alone time with your younger kids as you did with your firstborn when she was the same age. If your eldest child is playing a computer game, use the opportunity to look at books or do a puzzle with her little brother. Also resist the urge to compare your kids' development ("Gee, Betsy was already sitting up at 6 months, but Tara is certainly taking her sweet time!"). As long as your youngest is developing within the normal range, there's no need to concern yourself with whether she's advancing at the same speed.