The funniest (and most awkward) one I ever saw was at my neighbor’s wedding, her twelve-year-old niece walked down to Hey Dum Diddly Dum. No joke.
It’s fairly common. I’ve never seen it for a twelve-year-old though. For young children however, like four or five year olds, sometimes the family wants a cute tune for them to walk down the aisle to (and they’ll drop rose petals out of a basket as their walking or something). It’s a matter of personal taste.