Dreaming of being in the back seat of your son's car while your grandchildren are pushing it from the front can symbolize several things.

1. Feeling of Support: Being in the back seat might suggest that you feel a sense of support from your family, particularly your son and grandchildren. They may be playing a significant role in your life, helping you move forward in some aspect.
2. Lack of Control: Sitting in the back seat can also indicate a feeling of not being in control of your own life or direction. This may reflect feelings about your current situation where you feel dependent on others for guidance or movement.
3. Family Dynamics: The act of your grandchildren pushing the car could symbolize their youthful energy and enthusiasm. It may indicate that you see them as a driving force in your life, or it could represent your concerns or hopes regarding their development and future.
4. Transition: Cars in dreams often represent journeys or transitions. This dream could suggest that you are in a transitional phase, relying on family to help you navigate through it.

Consider your current life circumstances and how they might relate to these themes. Reflecting on your relationships with your son and grandchildren may provide further insights into the dream's meaning.