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.
I once asked my mom if my grandmother (her mother in law) was rich. Her reply: “No, but she likes to think she is.” I think she meant my grandmother spent money like she had plenty of it when she really did not. Can relate. I hope you do better!
"Watch the pennies and the dollars will take care of themselves." - Ben Franklin
This works with money and with other areas: Be faithful in the little things and the bigger things will take care of themselves. For example, if you don't get comfortable with telling little lies then you'll never tell big lies.
Check out from the library or Amazon: “My First Money Book: A Guide for Parents and Children to Saving, Spending, Sharing, and Investing Your Money” by Reggie Nelson
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.