At this point, the concept of money is not new to your kid of 7+ year old child. At school, teachers would have introduced them to the basic denominations of money– notes & coins. But they are yet to get the hang of the different other denominations and how the smaller value coins make up a rupee or a hundred etc.
What you need to know
The pre-requisite for this of course would be decimals. Once the children understand the concept of decimals then it would be easy for them to understand the lower denominations and the parts which make up a whole. The value of the money comes to their mind only during the later stages. But you can start developing the habit of saving during this age.
Your kid now will have an idea that everything you buy requires money. Enhance their understanding of money as you take them to buy groceries, fruits/vegetables or shopping. Focus their interest when you pay cash and receive change. They would definitely understand as they are now familiar with the addition and subtractions.