You can also help your children be good parents by being a role model for your grandchildren. Rather than lecturing, you can let your grandchildren (and their parents) see you living in a healthy, active and responsible way. You can eat right. Wear your seat belt. Be thoughtful. Don't litter. Treat people with respect and kindness.
The young ones will notice what you do. They will see how you behave and how you treat people when they go places with you. They will repeat things they hear you say.
Their parents should see what an impression you make and understand how closely children watch the adults in their lives. If you can make that point in a tactful way, take the opportunity. In this way, you can help your children provide good role models for their own children. The modeling passes from one generation to the next. Maybe by the time your own children are grandparents, they can look back and be pleased at the role model they've provided.