“I think it’s fun for them,” said Dr. Kohlbrenner, 58, a psychologist in private practice, who found out later that his son did not approve. “If you can’t do it when you’re a kid, when can you do it, you know?”

Dr. Kohlbrenner’s son, Justin, 30, said he and his wife felt that their oldest son was too old to be naked. “He was getting a little too big to be doing it, you know, especially in front of his brother and sister,” he said.

Experts like Sharon Lamb, a professor of mental health at the graduate college of education at the University of Massachusetts, Boston, said it’s all but inevitable that children will want to spend time wearing only their birthday suits, especially in certain situations. “Clothes can be uncomfortable,” said Dr. Lamb, a co-author of the forthcoming book “Packaging Boyhood: Saving Our Sons From Superheroes, Slackers, and Other Media Stereotypes.” “For some kids, getting dressed gets associated with something they don’t want to do, like eating their veggies.”

Around the age of 3 or 4, children begin to differentiate between what’s private and what’s public, experts say, and they usually begin to feel modesty soon after. But parents’ attitudes play the largest role in determining whether children are comfortable being naked at home, said Lawrence Balter, a psychologist at New York University and the editor of “Parenthood in America,” an encyclopedia.

“If someone has what appears to be an overly strong reaction to seeing young children running around naked, it tells us about their own hang-ups, their own inner conflicts,” Dr. Balter said.

Cultural norms are another factor. Katarzyna Psujek, 38, an administrator at Tiffany & Company and a mother of two sons who lives in Greenpoint, Brooklyn, said her son Sebastian, who turned 3 in May, often frolics at home naked and spent nearly an entire weekend naked last September at a rented house in upstate New York where the family celebrated a friend’s wedding with about 30 other overnight guests.

“Ninety-nine percent of the people who were there were Polish,” said Ms. Psujek, whose last name is pronounced SUE-yek. “I remember thinking, if there were more people around, and if they were Americans, would they accept him running naked as he was?”