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(CNN) Santa Claus is coming to town -- or so about 85% of young American children believe.

In interviews, 85% of 4-year-olds said that they believed in Santa, 65% of 6-year-olds said that they believed, and 25% of 8-year-olds said that they believed. Those numbers were published in a small study in the American Journal of Orthopsychiatry in 1978.

But researchers say those percentages of young children who believe in jolly old Saint Nick seem to have remained steady over the years.

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Research in the Journal of Cognition and Development in 2011 shows that 83% of 5-year-olds think that Santa Claus is real, the study's lead author, Jacqueline Woolley, wrote in The Conversation last year.

"We have found in more recent studies that that number of 85% sounds about right," said Thalia Goldstein, assistant professor of applied developmental psychology at George Mason University in Fairfax, Virginia.

"Children's belief in Santa starts when they're between 3 and 4 years old. It's very strong when they're between about 4 and 8," she said. "Then, at 8 years old is when we start to see the drop-off in belief, when children start to understand the reality of Santa Claus."

Nearly three-quarters of Americans say they typically received Christmas Eve visits from Santa as children, and one in five adults says they are the parent or guardian of a child in their home who believes in Santa, according to a Pew Research Center study published in 2013.

Outside the United States, how many children believe in Papa Noel? The percentage appears to be similar in some European countries.

Of 161 parents in the United Kingdom, 92.5% thought Father Christmas was real for their children up to the age of 8, according to a research paper presented at the annual meeting of the European Early Childhood Education Research Association in Finland in 1999.

It turns out that the more live Santa Clauses children are exposed to, the more likely they are to believe that he is the "real" Santa, according to a study published last year in the journal Cognitive Development

Goldstein co-authored the small study with Woolley, a professor at the University of Texas at Austin.

The study involved 77 children, 2 to 10 years old, who were interviewed after visiting a man dressed up as Santa Claus at a children's science museum in Norwalk, Connecticut. The interviews were conducted over the course of one week, before Christmas.

The interviews revealed that 39.2% of the children believed that the man they visited was the same Santa who came down their chimneys. An additional 38.8% didn't believe that he was the same person but thought he also lived at the North Pole and could communicate with the real Santa, Goldstein said.

Then, 13.8% said that the man was not Santa but that he shared characteristics with the real Santa, and 1.3% had a somewhat "adult belief," Goldstein said, in which they said that the man was not Santa and did not live at the North Pole but could communicate with the real Santa.

A limitation of the study was that older children who do not believe in Santa were excluded from the sample of participants since they "may have been reluctant to accompany their parents to this event," the researchers wrote.

"Age didn't predict whether or not they thought that live Santa was the real guy, and then we also found that what the parents were telling the children -- the amount of Santa activities and Santa promotion that the parents were engaging with -- also didn't affect whether or not the children believed that he was the real-life Santa," Goldstein said.

"The only thing that affected their belief was how many other Santa Clauses they had interacted with that year," she said.

On the other hand, age and cognitive development seem to predict when kids start to lose their belief in Santa, said Andrew Shtulman, a cognitive developmental psychologist and associate professor at Occidental College in Los Angeles.

"It's not a coincidence that children stop believing in Santa during the early elementary school years, because that's a time when they are developing more sophisticated notions of what is possible and what is not," said Shtulman, who has led separate research on children's belief in Santa Claus

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"In one of our studies, we asked children to brainstorm a list of questions to ask Santa, and we compared the kinds of questions they brainstormed to their ability to distinguish possible events from impossible ones," Shtulman said.

"We found that the better children did on our test of possibility judgment, the more skepticism they expressed in their questions," he said.

For instance, Shtulman said, children would shift from asking factual questions such as "how tall is the North Pole?" or "what are your elves' names?" to more probing ones, such as "how do you fit inside chimneys?" and "how do you know whether I've been naughty or nice?"

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As children move from belief in Father Christmas to doubt, most tend to feel proud that they have solved a sort of holiday puzzle, Goldstein said.

"They now get to be part of this sort of more grown-up group of people that doesn't necessarily believe in Santa Claus," Goldstein said.

"If a parent finds that their child stops believing in Santa and is really upset about it, there are other options," she said. "You can always talk about Santa Claus as being a spirit of giving. Or as a way to help others, or a way to think about people who maybe aren't as fortunate as you are."