Over the holidays we continued our family tradition of watching Elf, the Christmas movie in which Will Ferrell plays Buddy, an elf-adopted human who cavorts around New York in yellow tights. It gets better every year.

Over the holidays we continued our family tradition of watching Elf, the Christmas movie in which Will Ferrell plays Buddy, an elf-adopted human who cavorts around New York in yellow tights. It gets better every year.

One thing was different this go-round. Our kids have always liked to quote certain lines from the movie, but this year, Liam, who's now 8, was using the lines in ways that showed a deeper understanding of the humor. It was more than, "Remember when Buddy says, 'I'm a cotton-headed Ninnymuggins?'"

When he saw two of his teachers speaking quietly to each other, he went over to them and said, "I like to whisper, too." When we went to an event at the zoo, Santa was in attendance, but his beard was not convincing. Liam leaned over to me and said with a smile, "He sits on a throne of lies." The kid isn't just quoting humor. He's applying it.

Used to be my children were inadvertently funny in a "kids say the darnedest things" kind of way. There was the dorm-room-ready slogan Liam came up with a few summers ago: "Sometimes you lose, sometimes you booze." Or when he was a toddler and came running up to me with Bible in hand saying, "Daddy, wanna play God?"

That inadvertent humor still happens, but there's more intentional - and legitimately funny - humor going on now, too, which makes sense developmentally. In the '70s, researcher Paul McGhee studied 30 boys from Gahanna ages 5, 7 and 9 to find out more about cognitive development and children's comprehension of humor. McGhee surmised that "operational thinking" (a stage of cognitive development that happens between 7 and 11) was necessary to understand "incongruity humor" - i.e., when something is funny because there's an incongruity between what we expect to happen and what actually happens.

Among other things, McGhee found that the level of cognitive development was not "significantly related" to humor appreciation, but that for incongruity humor, operational thinking was important for interpreting and explaining it.

I think that's what's going on in my house. Kids can laugh at jokes and appreciate humor and silliness from a very early age. But being able to interpret why something is funny? That's a new level of understanding, and it's creating an ability to apply those interpretations to new situations.

Both of my kids have loved knock-knock jokes since they were little, but telling these formulaic jokes in the past somehow gave them the impression that any combination of silly words in the knock-knock format was hilarious. (That was always my cue to exit the room; I'm a killjoy when it comes to jokes that aren't really jokes.)

They still do the nonsensical thing from time to time, but they're now more interested in memorizing the correct wording for knock-knock jokes. They understand whythe jokes are funny, and they realize a proper setup and delivery are required for a good payoff. Here's my recent favorite:

"Knock-knock."

"Who's there?"

"To."

"To who?"

"To whom." (Deliver with raised eyebrows, cocked head and an air of teacherly disapproval.)

-Joel Oliphint is a freelance writer whose distaste for puns has always put him at a disadvantage when writing headlines.