From the first word to the first step, parents are the first point of education for children. You teach them how to ride a bike, how to rabbit ears help them tie their shoelaces, how to fight the monsters under the bed. You teach them the kind of person they should be by being the best person you can be.
If you want your kid to be polite, you show them how by being polite to others. If you want your children to be kind, you show them how by treating everyone from people of authority to service people kindly. With this train of thought, it would only make sense that if you want to teach your children to be frugal, you have to show them how by being frugal yourself.
Of course, as an adult, you know the advantages and disadvantages of using a credit card. Trying to discuss credit card VS cash pros and cons might not be easy when dealing with young children. While you can tell your kids that credit cards are dangerous if you're not careful, they'll better understand a physical representation of currency. Whenever you're shopping for food or for clothes with the kids, shop with cash. In the same way, if they want toys or treats, let them hold the money and see it leave their hands. Let them put coins in the metre or in a candy machine. This way, they see that it as something with value whenever they get something for it.
Have a Piggy Bank
If you have your own piggy bank, you encourage your child to have the same. Step up your game by opting for the clear, segregated piggy bank instead of the traditional ceramic one. This way you can label each slot with things that you want to spend for. You can label it the slots with simple things like Movies and Chocolates, adult things like car leases and mortgage (although, you might spend some time explaining what those are), or a little more abstract things like Emergency and Donations. You get to show your children that they can use money to buy things that they like but also to help others and have security. When they ask for a piggy bank of their own, challenge them by setting a savings goal.
Play Math and Money Games
If you hate math, you can relax. They don't have to be those complex genius games overachieving parents on the internet play with their kids. It can be as simple as letting your kids find the cheapest frozen carrots and peas they could find. That's sure to get them working on healthy competition and number skills. Get your kids to a math problem solving competition. It helps when you have little treats as prizes. Add a few math simple math quiz apps on their tablets or computers and walk them through for a few minutes a day. Join in on the competition for a few turns. Who knows, you might just get better at math yourself. Keep in mind that the more involved you are and the more fun the activity, the faster they'll learn.
Remember, your children will learn more (and faster) from you if you lead by example. If you turn frugality into a lifestyle instead of a lessons, your children will easily pick that up and take it with them as they grow older. Good luck!