Children must first learn the function of money before learning to spend and save money. Children can understand the simple concept of how money works when they are as young as 3. More often than not, a child sees a mother pays money and get something in return at a shop.
This understanding can be enhanced by repeated incidents and role play at home. Try showing your child using some money to get something in return.
When a child can understand this simple concept, you may educate him / her about ways to use money