As soon as your child asks "Why can't we buy that?" is time to start. Age 4–5, keep it simple: "We have money for needs (food, home) and a little for wants. That toy is a want, and we've used our want money."
Age 7–8: Introduce earning. Pocket money for chores (not for behaving, that's expected) builds the link between effort and money.
Age 11+: Talk about bigger financial concepts. Borrowing, interest, saving for a goal.
Teen: Tax, superannuation, budgeting, credit. Make it real—show them a payslip, talk about your household budget.