Let children know when you don't want them to buy something and the reason why. Be reasonable and evenhanded. This task can be especially difficult with siblings because of different needs, ages and circumstances. Avoid reference to your experiences with money as a child. Be patient, expect mistakes.
Children learn by trial and error.
Don't worry if it seems your child lacks money sense. It takes time to develop these skills. Encourage them to analyze what went wrong and why so similar circumstances can be avoided. Involve children in your money-making decisions. This provides excellent training in the techniques of money management.