How do you have sunday school without age-graded ministries?
Our Sunday School time is family-integrated. We have one Sunday School class that runs prior to our morning worship and in that class young children sit and learn beside their parents. The often will take a topic and teach on it during the class for several months. The class may consist of topics like: Old and New Testament Survey, Biblical Theology, Systematic Theology, The Ten Commandments, etc. The class is most often taught by one of our elders or interns.
This question also has a faulty premise. It assumes that children can't learn from the same people who are teaching parents because the material will be "over their heads." This is demonstrably false. We often have children and/or parents approaching the teacher following a class to ask questions or to make comments about the material.