As spies go, he is undeniably adorable.

The Elf on a Shelf, a rapidly growing phenomenon based on a 2004 book by Carol Aebersold and Chanda Bell, has become a beloved Christmas tradition for many families. The elf hides in a different spot in the home each day in the weeks before Christmas, reporting children’s good behavior and misbehavior back to Santa Claus. For many children, finding the elf’s new location each morning is a highlight of the season, while parents get to exercise a bit of creativity.

The elf is not, several privacy organizations were careful to clarify, the biggest threat the world faces.

But they find him creepy. Invasive and dangerous, even. They fear that the lanky elf is teaching children all the wrong lessons, acclimating them to being monitored by a police state, teaching them to passively accept constantly being watched by an unseen authority figure.

“I don’t want to sound like a Grinch, but we shouldn’t be celebrating seasonal surveillance,” said Albert Fox Cahn, executive director of the Surveillance Technology Oversight Project, a civil rights and privacy group. “It’s really a terrible message for kids.”

It is not as if Santa didn’t have eyes on children before the elf’s arrival. Considering he sees you when you’re sleeping, knows when you’re awake and knows if you’ve been bad or good, Santa has long relied on a robust surveillance network for his naughty-or-nice judgments.

The Lumistella Company, which owns the Elf on the Shelf brand, said the activity offered entirely wholesome benefits.

“Santa’s Scout Elves don’t just help to keep up with the Nice List; they also share with Santa how families are spreading the spirit of Christmas,” the company said in a statement. “Many children note that their favorite moments throughout each season include waking up to see where the family’s Scout Elf has landed and the humorous scenes they sometimes set up. Our hope is that the Elf on the Shelf will create cheerful holiday moments and precious family memories that will last a lifetime.”

But those who focus on the danger of surveillance in the everyday world find something sinister about the elf. They look beyond those cute, blue, very dilated eyes and see a presence they would never invite into their homes.

“I know a lot of families just see this as a fun thing, but it’s worth thinking about the messages it’s giving to children about surveillance by authorities,” said Jay Stanley, senior policy analyst at the A.C.L.U. Speech, Privacy and Technology Project. “Personally, I consider success as a parent to be teaching my kids to do the right thing even when nobody is watching, whether they be from the North Pole or anywhere else.”

He added: “Maybe these are elves that should be left on store shelves.”

Caitriona Fitzgerald, deputy director of the Electronic Privacy Information Center, a public interest research group, said children need private spaces to grow up with a sense of autonomy and independence.

“If kids think they are always being watched, even when the watcher is a magical elf, that can have real effects on how they see themselves in the world,” she said.

Mr. Cahn, of the Surveillance Technology Oversight Project, said children should be taught that “no one should be looking at you in your bedroom without consent.” There is a cost to normalizing surveillance, he said, “even in the most adorable ways.”

“I don’t want to be the first one to take Santa Claus to court for invasion of privacy, but consent matters, and having privacy matters,” he said.

The elf has also become a presence in classrooms, with teachers opting to bring him to school as a December activity for young children.

Liz Janusz, an instructional coach in Los Alamos, N.M., said she did not believe the elf belonged in schools, largely because it excludes children who don’t celebrate Christmas. But, Ms. Janusz added, she loves the tradition for her children — it just requires a slight recasting of the narrative.

“In our own house, we say the elf is just reporting wonderful, kind deeds you do, rather than focus on the naughty,” she said.

Heather Flannigan, the mother of a 16-month-old girl in Aberdeenshire, Scotland, said she was looking forward to hiding the elf for the first time next year. The surveillance bit, though, doesn’t sit right with her.

“I want her to be a good person because she’s a good person, not because someone’s spying on her,” she said.

The elf was a subject that at least some privacy organizations, which typically focus on the deadly serious consequences of overstepping governments and the creeping reach of technology companies, had a bit of fun discussing.

Calli Schroeder, the global privacy counsel at the Electronic Privacy Information Center, responded to a reporter’s questions about the elf with lyrics, to be sung to the tune of “Santa Claus Is Coming to Town.”

It begins: “You better watch out / Look up on the shelf / Don’t accept spies just because they are elves / Santa’s spy is watching your kids.”