It’s fine, great, to be thrifty. But please don’t be cheap. Hard-earned money should neither be squandered or hoarded. Enjoy your success! But save more than you’re comfortable with. It’s like my running coach used to say: Keep going until you feel like you’re gonna poop your pants, then push yourself to do another mile. Point is, it should hurt a little.
Have them sort change, and eventually to count it. It teaches them to gather things that are alike, it's an introduction to money and it occupies them for 15 minutes! Just make sure they're old enough to be past the point of putting coins in their mouth.
Practice “going without.” Talk about how nobody gets what they want all the time. We should learn how to just choose to go without something we want. Get them in on the discussion and pick something every day to do without.
Start a yearly “review” right before school year. Raise allowance as appropriate. If they want more money, they’ll have to take on more responsibilities.