Dawn Landau and her son Robert

In this story:

• Older parents, divorce decreasing number of children
• The effects on a child
• What to tell the children

From CNN Medical Correspondent Rhonda Rowland

ATLANTA (CNN) -- Is there a perfect family size? Prevailing wisdom would probably indicate at least four: a mother, father and two children -- a boy and a girl.

But for many, the family is smaller. U.S. Census Bureau records indicate close to one in five families have just one child.

"I always thought for sure I would have two, growing up," Dawn Landau said.

But that's not the way life is turning out for Landau and her husband Doug, parents of one child, Robert, age 6 1/2.

It hasn't been an easy decision. The Landaus said they frequently have had serious talks about adding to their family.

"I've bounced back and forth between what would be best for Robert, having a sibling and somebody to grow up with and have when we're gone or to help care for us in our later years versus our ability to be able to just get up and go," said Dawn Landau.

For Doug Landau, the decision has been one of economics.

"The standards for what our parents set for us, you know, giving up everything for your children has translated for me into, 'Hey, I want to make sure it's perfect for my child,'" he said. "And nowadays, that becomes a financial issue."

"One child, you know you can do it. Two children, maybe."

Alexis White and her father

Experts say there are other reasons for the increase in only children -- a high divorce rate and couples starting their families later in life.

For Carolyn and Chuck White, infertility became an issue. After they had daughter Alexis, Carolyn couldn't become pregnant again.

"I think when you choose to have an only child, and it's a conscious choice, you don't have that nagging feeling inside you," Carolyn White said. "You know that when you made the decision, you made it because it was right for you."

"I didn't make the decision. It was made for me, and I think that is a lot harder."

Having an only child can be difficult for another reason: There is a sitgma, a stigma attached to only children.

Experts say it goes back a hundred years when a researcher did a study called "Peculiar and Exceptional Children." He concluded being an only child is a disease in and of itself. So the myths persist.

"The spoiled, self-indulgent, self-centered little brats sort of thing," said Chuck White.

However, recent studies don't support those myths.

"Studies show that only children often have higher achievement levels," said psychologist Jane Annunziata. "The only children score high on the sociability indexes, as they're called, in terms of social relationships with peers."

"And that, in general, there's not a lot of difference between only children and firstborns."

But experts and parents say there are potential pitfalls in raising only children.

To offer other families guidance and support, the Whites started a newsletter and Web site called "Only Child."

"Only-child parents try to run interference on virtually every level in every facet of a child's existence, and that's really not fair because it really leaves a child open for all sorts of disappointments -- major disappointment," said Chuck White. "If you don't get a child involved early on with as many peer situations as possible, you're in deep trouble."

Parents say they also have to resist the temptation to over-indulge a child.

There's also the inevitable question: "Why don't I have any brothers or sisters?"

Alexis White, 18, admits she wanted siblings.

"I wanted them because my friends had them, not because I needed them or really wanted someone to play with."

To help parents deal with the sibling question, Annunziata co-wrote a children's book on the subject, "Why Am I an Only Child?." The book tells of a little rhino who wants a baby brother or baby sister.

"[Children] feel mad that they don't have a brother or a sister sometimes; sometimes they feel sad; sometimes they feel lonely," Annunziata said. "Mostly, they don't understand why, and they need help to understand. So we wrote the book to answer some of those questions."

Friends are extremely important for only children.

"I am very attached to my friends, not in an unhealthy manner, but in a way that I mean they're my family," said Alexis White. "That's what I have -- I have my parents; I have my friends."

But what is it like to be the parents of one child?

"Selfishly, I think it's kind of really cool for a parent to have an only child," Chuck White said.

"I really like the fact that I can have a life for myself and have enough time to have a great time with Robert," said Dawn Landau.