The Serie A club let 12,200 children sit at both ends of their stadium for Sunday's match against Udinese but the rowdy kids behaved little better than the ultras and Juve were fined 5,000 euros (£4,100) after they shouted abuse at Udinese keeper Zeljko Brkic every time he took a goal kick.
"Juventus were fined after their (very, very young) supporters repeatedly aimed an insulting chant at a player from the opposing team," Serie A's disciplinary panel said in a statement.
The children were copying a popular ritual in Italian stadiums where the visiting goalkeeper is insulted whenever he takes a goal kick.
"I wanted to say something right after the game because it bothered me but I didn't want to put any oil on the fire and I decided to stay quiet," Udinese coach Francesco Guidolin told Italian media.
"For a club such as Juventus where everything is beautiful, in particular where the stadium gives you the idea that you are not in Italy, it is really troublesome to hear those words every time the goalkeeper puts the ball into play."