IT started as a gag: spaghetti tacos.

On an episode of the hit Nickelodeon series “iCarly,” the lead character’s eccentric older brother, Spencer, makes dinner one night. Glimpsed on screen, the dish consists of red-sauce-coated pasta stuffed into hard taco shells. What could be more unappealing?

When Julian Stuart-Burns, 8, asked his mother to make the tacos one night, she simply laughed. “I thought he was joking,” said Jennifer Burns, a Brooklyn mother of three. “But then he kept asking.”

Ms. Burns finally gave in  like thousands of other moms  and cooked up the punch line for Julian’s birthday party.

That punch line has now become part of American children’s cuisine, fostering a legion of imitators and improvisers across the country. Spurred on by reruns, Internet traffic, slumber parties and simple old-fashioned word of mouth among children, spaghetti tacos are all the rage. Especially if you’re less than 5 feet tall and live with your mother.