"I see dead people."Very few people didn't shudder when a little boy in the movie "Sixth Sense" whispered those four words, and there's not a parent out there who didn't look at their own children with concern - especially the ones who have imaginary friends.

But "Mom, you forgot to pour juice for Keisha, too" is not crazy talk. It's a healthy way for children to explore fantasy and reality.

Up to 65 percent of children develop an imaginary friend between the ages of 3 and 5, said psychologist Rob Pennington of Mental Health America of Greater Houston.

Basically, it comes down to biology. Simply put, Pennington said, we have one brain that's split in two halves.

"The left half has to do with the physical world and the right half has to do with an imaginary world," Pennington said. "We function in these two worlds all the time, but kids don't know they're supposed to keep them separate."

Most children outgrow imaginary friends by the time they go to kindergarten, but about one-third keep them close through age 7. Some imaginary friends gradually disappear, others as spontaneously as they seem to appear. Houstonian Sue Payne said her daughter Hannah's imaginary friend "Tony" stayed behind when the family moved from D.C. to Texas.

More Information

Imaginary friend facts

Children with imaginary friends are:

exploring the worlds of reality and fantasy

aware of what's real and what's not

highly creative and empathetic

likely to display advanced vocabulary and cognitive skills

going to outgrow it

Hannah, now 25, doesn't recall Tony beyond her pre-K days, but the long-term effects have been quite positive. Research shows that children with imaginary friends tend to have above-average vocabulary skills, sharpened cognitive skills, oodles of creativity and buckets of empathy.

"Hannah's teachers told me they would ask her to sit with other kids when they were having meltdowns, because she had an ability to connect with them," Payne said. "Maybe the ability to work things out with her imaginary friend helped develop this?"

She may be right.

"For a child to have an imaginary friend, they have to imagine the perceptions of someone else, even if that someone else is imaginary," said Dr. Elizabeth Newlin, program and medical director of the Adolescent Treatment Program at The Menninger Clinic in Houston.

As children grow and begin to experience more complex social situations, their imaginary friends may also take on new identities and traits. And the friend isn't always of the human variety - some kids describe animals, others talk about superheroes.

The younger the child, the more likely the imaginary friend is based on a physical object, such as a stuffed animal. Girls are more likely to have an imaginary friend than boys, but the reasons for having imaginary friends in the first place are quite varied. Some kids like to have a scapegoat, someone else to blame if they're caught misbehaving or in a lie. Some kids need a confidante, someone to help them cope with changes such as a new sibling or a move. Some kids want a role model, someone who will show them the way when things seem complicated.

While there are several positive things about imaginary friends, there are a few things that may indicate an underlying illness such as schizophrenia.

Pennington said it's not so much the existence of an imaginary friend, but the extent of the role it plays in the child's life. If the child is not able to interact with others, seems afraid of the imaginary friend, shows sensitivity to light and sound, rapidly and frequently changes the subject, or says the friend is telling him to do hurtful or violent things, a visit to the pediatrician is in order.

But if a child invites siblings or parents inside this imaginary life - requesting an extra place setting at the dinner table, reminding you to buckle the friend's imaginary seat belt too, for example - all is probably well.

It's up to parents how much they want to embrace, encourage or tolerate an imaginary friend, but, as with most things in parenting, patience is a virtue.

"If you want to speak to your child about it, don't do it while they're playing," Newlin said. "Once you demand to know where this came from, their play will collapse and they will no longer enjoy that time. You just spoiled the party."