Fun for elementary Spanish. Even if it's not a required subject I think I would still try to incorporate it because kids learn faster and retain that information better than adults. Maybe have extra credit quizzes on it or something.
Sub Tub Sub Plans Kit for Elementary Spanish Class- create your own Sub Tub! Printable Spanish Activities and Instructions for making your own sub tub! Perfect for young learners! Mundo de Pepita, Resources for Teaching Spanish To Children