Toddlers often have imaginary friends. But mental health professionals have long believed that school-age children rarely do and that if they do, immaturity or even deep psychological conflicts may be the cause. Quite the opposite may be the case.

A study has found that two-thirds of children ages 6 and 7 report having had an imaginary friend - and that many still have the pretend playmates. These made-up pals play a key developmental role during the early school years, researchers say.

“These characters serve an emotionally healthy function, and pretending is an important part of developing social and cognitive abilities that remain with us throughout our lives,” says Stephanie M. Carlson, a study coauthor and a psychologist at the University of Washington in Seattle.

In an earlier study, researchers at the University of Oregon interviewed 152 preschoolers, ages 3 and 4, and their parents about whether the children had imaginary companions. In a follow-up conducted three years later, when the kids were ages 6 and 7, 100 of these children and their parents were again interviewed.

Researchers found that, overall, 65% of the children had an imaginary companion at some point in their lives and that 31% of school-age youngsters played with these fantasy friends.

The study also revealed that this activity improved cognitive abilities because it forced children to deal with multiple possibilities. In addition, school-age youngsters who had imaginary companions scored significantly higher on tests of emotional understanding of others and social development than children who didn’t.

The study appeared in the December issue of the journal Developmental Psychology.