It is the utmost responsibility of the parents to teach their children about the value of money and how smart they can be with their money. Smart spending habits and Investing habits are not taught at schools. It is at home the kids learn these aspects.
It is better you educate your kids on the value of money as soon as they start counting. You can let the child know the things you cannot afford. Though the concept of "We cannot afford it" can be detrimental to their mindset, you have to make them think that rolling in riches is not the way to be financially happy. You should restrict the kids from doing certain things which may be fun to do. This can help you teach the kids about intelligent financial decisions, in a better way.