Your grandchild may or may not be able to drive a car. It is best to get them accustomed to riding public transportation at an earlier age, just in case. First you want to get them used to just getting on the bus/subway and sitting still. So you start on days when it is not so crowded. This will be a disorienting experience for them because it is so loud and smelly. However, eventually, they will be focused enough to practice paying the fare. Then you can attempt to do trips at rush hour times. Then you teach, to pay attention to where the bus is going, and how to know when their stop is coming. Make a conscious effort to travel to different places on different bus routes. You do not want them to start insisting on a familiar trip. As they get older, you teach them how to map their trip and how to time it, so they can get to their destination on time. Start out with trips to their favorite places. This will make it a happier experience for them.