CHICAGO - For Kelly James-Enger, breaking up battles between her two children is a year-round job. But lately, the Downers Grove, Ill., mother has enjoyed a little help from a wide-eyed elf named Michael.

"I say, 'You two need to stop fighting, or Michael's going to go to the North Pole and tell Santa,' " said James-Enger, one of many parents who have adopted the tradition of The Elf on the Shelf, a popular children's book that promotes the idea that Santa sends elves to watch kids and report good, or bad, behavior.

An estimated 6 million copies of the book and its accompanying red elf toy have sold since it was released in 2005. Parents ask their children to name the elf, help the doll "magically" appear in a new spot each morning, and often share elaborate hiding-spot ideas on Facebook and Pinterest. A parody, "The Elf Off the Shelf," and "inappropriate elf" images on Google and YouTube also have fueled its popularity.

"Almost all my girlfriends have one," said James-Enger, who estimates that her children, Ryan, 8, and Haley, 3, argue 10 percent less in December thanks to Michael's monitoring.

But some parenting experts and booksellers question the discipline tactic and its popularity.

"I don't think that's a very good strategy," said Margret Nickels, clinical psychologist and director of the Erikson Institute Center for Children and Families in Chicago. "It's the parents who want to be in charge as the authority in the house. Not the elf or Santa Claus."

At Anderson's Bookshops in Naperville, Ill., managers refused to sell the book for several years but relented after customers' repeated requests. The store now carries The Elf on the Shelf, which retails for $29.95, but employees won't recommend it, said Becky Anderson, co-owner of the independent bookshops.

"From our standpoint, we think it's a little creepy," Anderson said. "We think there are other ways to create a family tradition."

The Elf on the Shelf story went to print after Carol Aebersold, a retired music teacher from Atlanta, lamented that she felt useless after her children grew up and moved out.

Then one day, one of her adult twin daughters, Chanda Bell, saw a familiar elf doll perched on Aebersold's kitchen shelf. She suggested that her mother share the tradition their family had enjoyed for years, said Aebersold, who cowrote the book with Bell and is promoting a second book under the trademark.

According to the tale, the elf observes children's behavior all day and returns to Santa while they sleep. To maintain the magic, children must never touch the elf. Parents help the elf find a new spot to surprise the children each morning.

Today, Aebersold, 65, said she is amazed at the merchandise her story has inspired, including coloring books and clothing. The kits are sold in stores nationwide, and the 50-employee company behind them contracts with several major retailers.

"It blows my mind, but I feel so good knowing that I am actually leaving a legacy for my grandchildren," she said. "And I am in awe of the creativity of some of these moms and dads who have come up with the things for the elf to do."

Janice Kowalski, a child psychiatrist at Linden Oaks Hospital in Naperville, said some children might be spooked by the idea of an elf watching them. That happened to her daughters when she introduced the tradition, at their request, years ago.

"You definitely just have to be aware that they might get anxious about thinking somebody's in the house. If that happens, you maybe don't want to use the toy."

In keeping with the story, Aebersold noted that the elves don't watch children while they're sleeping. That's when they return to the North Pole to give Santa a report, she said.

Aebersold said she avoids viewing online parodies of her book. "I would just like it to be more pleasant and fun and something the kids really look forward to every year."

And that's just what it is for Ryan and Haley Enger, who take turns talking to Michael about their activities, their holiday wish lists, and other news. James-Enger is enjoying the magic while it lasts.

"To me, it's truly less about discipline and it's more about the excitement of finding him," James-Enger said. "It's kind of like Easter morning every morning in December."