For this same reason, we pay our kids allowance in cash and when they buy toys or other things with it, we make sure they are the one to take the cash out of the little cash purse, carry it in their pocket to the store, and they are the one to physically hand the cash over the cashier.

I don't care if it would be 10x easier and I'd get 1.5% cashback on the purchase with the credit card; I want them to have the experience and understand that they are trading away a limited resource that took time and effort to acquire, not just mindless swipe/stick/tap.