A book I read well over 30 years ago, and is still apparently updated today, is "The Kids' Money Book" by Neale S. Godfrey, which you can certainly find secondhand for cheap. There are updated versions authored by Jamie Kyle McGillian, and so long as they are in the original vein they are probably excellent.
However it's not something I would throw at a 6-year old. A sharp 8-year old should be able to grok all of it though.
However it's not something I would throw at a 6-year old. A sharp 8-year old should be able to grok all of it though.