We held a workshop on financial education, and the starting point was "The story of money": where it came from, how things were swapped for one another before coins existed, and why something everyone would accept became necessary.
It is one of the few economic explanations that works perfectly at this age, because it can be played out. When you try to barter and cannot find anyone who wants exactly what you have, the problem becomes obvious within three minutes — and the solution, namely money, arrives as a relief rather than as a definition to be learned.
Then we made the bunny piggy bank, where the children at the PlusKids after school were going to keep their savings. A piggy bank is not a decorative object: it makes visible something that otherwise stays entirely abstract to a child. Money set aside can be seen, heard and watched growing — and the difference between spending today and saving up for something else suddenly becomes a real choice.
The habit of saving is formed early, and it is formed through practice rather than advice. All the better if the practice has bunny ears.