They should by now, be learning about money at least in school. My daughter is the same age and they learned it in school since Kindergarten. She's in first grade now.
A good idea is, to get a bottle or bank... and whatever money or coins she is given or earns.. she can put it in there. There are "kids banks" that have a digital read out and tells the child how much money they have in the bank. You can find it on amazon.com
For us, since my daughter was 3-4 years old, we give her some coins or a couple dollars here and there... and then IF she wants something, she has to choose, and see if she has enough, and we "help" her by looking at the price tag versus how much cash she has... and then we problem solve it. But also by now, she knows her numbers and which is "bigger" or "less than." She has gotten very wise about making decisions this way. And, she is also a good "saver" and will choose to save her money too, instead of just spending everything. She will even save her "tooth fairy" money in her bank.
It's all about exposing them to it, and helping them "evaluate" it in reflection to how much money they have... and math skills, number skills, number recognition etc. That is the way my daughter's Teachers teach them too.
For "earning" money at home... we don't apply it to EVERY SINGLE CHORE she has in the house... that would be too overwhelming for such a young age. BUT, for certain things, like making her bed, picking up her clothes, helping to wipe the table after dinner... we give her a few coins from a container that we have. Or, we give her a dollar. If she is "naughty" or does not do something... we don't necessarily deduct it from what she earned... because she DID earn what she earned... but, if the transgression was "big" enough... then we might take back .50 cents. We put a flat rate limit on it.
But, we don't expect "perfection" in her everyday, every moment behavior. I feel that's too rigid. Main thing is she try "her best" and that is good enough.
It's up to you to decide "which" tasks will "earn" money for her... and which won't. It does not have to be "every little thing" that they do. But just choose a few manageable "chores" that is do-able for a child that age. It HAS to be age appropriate. Or, no one gets anything out of it.
When we go out, and if she asks to have something.. we tell her "well, do you have money in your wallet?" (we gave our girl her own wallet since about 3 years old). Then she will go and look and we have her count it. THEN, based on how much money she has, we let her buy something. If she wants something that is 1-2 dollars more than she has... I will put in that money for her. Its okay. But my daughter is always reasonable, and "spends" wisely. We just have always discussed things like this with her. And sometimes, I will just tell her "I don't have money today. Sorry we can't buy anything." And she understands.
We also teach her about how we get money... we work for it and have jobs etc. What is a bank machine? We explain that to her too. She knows, that money is not endless and that it can run out, and we have "bills" to pay. We also explain to her that things like leaving on the lights, or running the water too long "costs money." And she also learns about how to conserve energy in school too. SO, it is understandable for this age. But you have to explain it to them in everyday activities, and show them. Its all about exposing them to the concepts and in daily life.
Kids really benefit by learning it early.
Good luck, hope this helps,
Susan