I recently volunteered with an organization which teaches students about financial literacy. Its called Junior Achievement and they make it really really easy to volunteer. They give you all of the lessons including cool games and activities. My favorite was a budgeting activity.
1) Each student was assigned a job with an average salary
2) Compared net and gross salary
3) Created a budget by saying "many people spend 25% of their net salary on housing. What is 25% of your salary? Repeat for clothes, food, transportation, entertainment, etc"
4) Then they got to go around the room to different posters. Each poster was for a different category. So one poster was for Housing. It said "you can spend $3000 on a mansion, $1500 on your own small house, $750 on a shared apartment or $200 to live with your parents?" And each student could say "well, 25% of my net budget says I have $1200 available, but I underspent on my car so I'd like to live in a small house."
5) after they selected some level in every category, we calculated how much left over they had for savings and charity (we had them target 20% for retirement and other things you save for like vacations and emergencies. I know its not mustacian, but it wouldn't raise red flags with teachers or parents).
We did this in a 7th grade class (12 year olds) and it was a huge hit. It even got the uninterested kids involved because we got to plan out their budget as "twitch.tv video game streamers" (don't need transportation or entertainment but they probably still need food)
Basically, if you want to help kids learn this stuff, check out Junior Achievement, they do an awesome job.