Since C was born, we've dropped all our spare change into a piggy bank. When N was born, I added another bank and split the change between the 2. Whenever I pay cash for something, I always pay in paper money and take the change home. (side note: great new baby gift/idea for new parents! We've saved literally hundreds of dollars over the last 5.5 years by saving the spare change!)
Once they were old enough, I would save it up for a while, and then allow them to drop the change into their piggy banks. I figured among other things, it helped build fine motor skills.
In the last few months, the original piggy banks were full, so I changed over to using large mason jars with a slit cut in the top. We've also been working on learning more about money - so we take the jars down and separate the different coins out and they exchange their coins for paper money. They're learning the different coins and their monetary value. They understand that 100 pennies equals a one dollar bill, etc.
Another thing I've started doing is paying them for chores. I have read various things about how important it is for kids to do chores to be part of a family vs. the importance of learning the importance of earning spending money. I've decided I fall more into the importance of earning money for jobs well done. While I don't necessarily receive a paycheck for taking care of my family & home - I do have the ability to take money from our budget to purchase things for myself and the boys. I decided it made sense for them to have more of an understanding of how money is earned and spent. This way they can purchase their own small items when we're out and plan their purchases. I don't think they're too young for that. C definitely thinks twice about his purchases now that I can tell him that something costs the equivalent of making his bed for 30 days!
I pay a dime to each boy for making their bed and bringing their night-time cup into the kitchen each morning. They have made their beds in the past - but never with the excitement and creativity that they are now! They arrange their stuffed animals in different patterns every day. As long as their bed is made before bedtime, they earn a dime.
I debated about keeping a chart and paying them for a week's worth of work - but I think they're too young for that. It means much more for them to receive their "pay" immediately after a chore is completed.
They also earn a dime for picking up their bedroom. At this moment, they're earning a nickel each for picking up each and every plastic animal in the playroom. (and they will continue earning nickels for all the different items that need to be picked up in there - I have closed the door to that room for TOO long!)
It's amazing the different attitude they take in completing chores. They're excited about it, and talk with each other about ways to make the jobs easier and/or faster. N has negotiated with his brother to make his bed and then C earns 20 cents for bed making. It doesn't happen every day, so I've let that slide for now.
I think as they grow, I will shift to specific weekly chores, and paying them once a week. We have also talked about savings, and I need to take their original piggy banks to the bank to deposit into their savings accounts. And, then there's charity to consider - they are familiar with our tithing at church and donations to the food bank and other places - but I want them to participate in it with their own money.
This is definitely a work in progress. It will continue to evolve and change over the years. I hope to instill in them a good sense of money management - something DH & I still struggle with at times.