Take the family on periodic “spending fasts.”
As an exercise, go a day, a weekend or a week without spending any money. Make due with what you have.
Encourage participation. Tie in spending fasts with holidays, lent or in support of a cause.
There are things you should not say:
Never comment or ask a woman about her age or weight.
Never comment on how many kids someone has (or doesn’t have.) The size, timing, composition, etc of someone else’s family is not your business to weigh in on. You never know who is struggling with loss or infertility, etc. And if someone announces they are expecting their seventh kid, the only correct response is “Congratulations” “How are you feeling?” etc. Just like you would if it was their first. Never ask someone how much weight they lost. If they’ve lost weight, just say “You look wonderful/amazing/ fantastic, etc.” And of course never comment on anyone having gained weight. Just say “You look wonderful.” And never never never ask someone how much money they earn or how much money they have, or how much they owe or paid for something, etc. People’s finances are personal, and are just not any of your business.
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.
"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.
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.