These basic astronomical concepts are misunderstood by the majority of the population. In the course of Project STAR's research, it was determined that the majority of Harvard graduates did not understand the cause of the seasons, the moon phases, and the fact that the earth revolves around the sun once a year. The most common misconception is that seasonal changes in climate are caused by the changing distance of the earth from the sun.
The Project STAR textbook and activities are good on these points -- or just use simple, hands-on models.
In some jurisdictions, it is common to repeat the teaching of the seasons, phases of the moon etc. in grade 9 (with little success). You may want to review briefly -- or do a diagnostic test.
The following activities may have been done in grade 6:
Activities: Modelling Day and Night, Seasons, and Moon Phases. These activities can be done indoors with light bulbs and styrofoam balls; they enable students to experience the 3-D nature of these phenomena, to ``discover" eclipses, etc. Keeping in mind that people have deep-seated misconceptions about these topics, you should devote adequate class time to these if you do them. 2D pictures, videos, and computer simulations are of limited use.
There is an ingenious device called ``Pipehenge" -- a kind of ``jungle gym" invented in New Zealand, which allows the student to be at the centre of a model of the motions in the sky; see: www.pipehenge.com A desktop version is now available.
Activity: Modelling 3-Dimensional Illumination Outdoors. . A good example is the following: choose a sunny day when the sun and moon are both visible in the sky (in the afternoon when the moon is near first quarter phase, or in the morning when the moon is near last quarter phase). Hold a ball in your hand so that the sun shines on it, and extend it toward the moon. You will see the ball and the moon illuminated by the sun in the same way, and for the same reason. The ball and the moon are both round objects, illuminated by the sun. This activity can be done in a few minutes.
These concepts are so basic that it is worth teaching them right, i.e. monitoring the students' preconceptions, and being absolutely sure that they understand the concepts, and can explain them from their understanding, and not just from their memorization.