I was out shopping with my son not too long ago and he asked for a toy and I said no (sometimes you actually have to say no - even if you can afford it).
He asked why and so I used that as a teachable moment.
I said that toys cost money and that Mom and Dad work to build up a pile of money and that everything we spend money on takes away from that pile.
He said then I should just use the credit card!
It dawned on me right then and there that kids these days see us use our credit or debit cards (and not cash) so they don't really have a chance to witness and make the connection between spending and cash.
I suggest that we parents use CASH occasionally to buy stuff to show the kids that stuff costs money and its not some magical process of swiping a plastic card and getting stuff.