When your child reaches 5 years old you can begin giving them an allowance.
Although I've given my kids a little bit of money when they were 2 years old to 3 years old and even 4 years old but I only gave them a few dollars and was teaching them what they could buy with it.
They were very happy when they got a little money and could use it to buy something on their own and take the item to the cashier and pay for it with their own money.
Of course I was there but they loved being able to pay for something on their own with money they have had.
Once a child reaches 5 and beyond they begin grasping the concept of money and it's a good way to teach them how to manage money.
As soon as they can count money it's good to start giving your kids an allowance and teach them about spending the money and saving the money.