In the United States today, more than 20 percent of parents have an only child. There are many reasons why families with only children are more common today than they were 50 years ago, when larger families were the norm. People are marrying later (or divorcing earlier), are waiting longer to start families, have more and better access to birth control, and often make career choices that don't accommodate having more than one child. Many parents are also simply deciding that one child is family enough.