You don’t need to teach kids about marriage.
A child must be taught that each person is different – “Just as their faces are different, their thoughts are different too.” A child must be taught that in order to cultivate healthy relationships, one must respect the other, and that specifically includes respecting those differences. A child must be taught to give to others, because this is what we do. A child must be taught to be grateful and to show appreciation. A child must be taught that friends, parents, siblings, etc. are not personal servants, but people with their own lives, people who are “the protagonists in their own movies,” insofar as the child is in his/hers. A child must be taught to communicate feelings properly. And so on.
Marriage does not need to be taught. Life does. Someone who has learned about life will figure out how to handle marriage.