Including your child in errands that involve the handling of money makes for an amazing tool,and teaches valuable financial skills.
Involve your children in the family budget,explain where the family income goes,then teach them how the budget effects their family,and that how you grocery shop etc affects everything else.
Giving them a small amount of money every week to bank will help,they will learn to add it all up at the end of the month,and when they can spend it you can have them buy 2 or 3 different items and add up what they have left etc.
I beginning homeschooling my children next year,my eldest will be in grade 2,and is right now learning about coins and money in general at school.My daughter is more aware of the value of money and that it is how we provide for our family,but she has yet to learn it's origin.I will research the history of when money first became a form of trade and value and teach that to my children.
Buying fake money is great as a resource,letting kids play with it,buying items from one another or you and giving change.
It all comes back to them having a simple knowledge of numbers in itself,and using them in financial context.