When it is relevant for a client, PWR financial plans include a section on personal finance for children. We compile information from a few sources including Money as You Grow.
Here are some age appropriate activities I started doing with my 3 1/2 year old.
1) Identify what costs money versus what is free. For example, we pay money when we go to the local pool. We don't pay money when we go to the library, park or the beach. Those are free activities.
2) Explain that people can get money by working. Mommy and Daddy go to work to get money. A couple of neighborhood kids were selling snow cones one day - they were working too!
3) There is a difference between what we need versus what we want. We need to buy fruits and vegetables at the store or farmer's market. We don't need to buy lollipops and cookies. Those are special treats we get every once in a while. We need a place to live and a car to drive, but we don't need an automatic bubble maker (yes - these exist!) or a new scooter. Those things are nice to have, and we may want and enjoy them, but we don't need them.
Use these examples or create your own using the Money as You Grow site as a start.