Earlier this week, a woman wrote in to Slate's Dear Prudence advice chat asking whether it's considered lying to allow her daughter, who is three, to continue to believe in Santa Claus.

Prudie's take: Nah.

"Reality will eventually out," wrote the columnist, Emily Yoffe, "but there’s so much reality in this life, that one of the delights of childhood, and of being a parent, is to spread a little fairy dust occasionally."

Later in the chat, though, another person wrote in saying that his or her parents kept the Santa thing going until the writer was nine, at which point this person found out and felt "incredibly embarrassed" that he or she had been "duped" for so long.

The takeaway is clear: There is no way to not traumatize your children.

So, barring an early reality check from an elementary-school Scrooge, when is a normal age for kids to realize who's actually leaving those presents under the tree?

In studies for which she interviewed children, University of Texas psychologist Jacqueline Woolley noticed a drop-off in belief in Santa after the age of five. That's also when belief in the Tooth Fairy peaked, as well:

Percent Who Believe, by Age

Her findings resembled a 1978 study that found that 85 percent of 4-year-olds believe in Santa, but only 65 percent of 6-year-olds and 25 percent of 8-year-olds do.