Tai Chi (like all martial arts, yoga, Pilates, etc.) is a movement program that has been developed and honed over years and through many forms. An instructor needs to have experience and knowledge that require years of study and training. If you are serious about providing your students with some Tai Chi instruction, find a qualified Tai Chi practicianer in your area and ask them to come into your class for an introduction of the art for your students.
I enjoy taking classes in Pilates, yoga, tai chi, gyrotonics, and a few other systems, but I know that I am not qualified to teach others these classes.