I noticed two different situations at the grocery store today. The first one was a mother and her daughter (who was about 10-11 years old). The daughter had the grocery list and checked off the items as they found them.
The other was at the checkout, there was another mother and her daughter about the same age (10-11 year old). They were in the line next to me and I got there as they were paying. The daughter swiped the credit/debit card through the machine. This is fine if she realizes where the money comes from. In many cases, kids see their parents using credit cards or writing checks and they think that is all that is to it.
I have posted before about using real life experiences to teach children about money, etc. Both of these situations are perfect examples of this. As long as you explain where the money comes from.