clearheaded:
Suggestions on the Kav HaYashar (take what you like, leave what you don’t, some may be contradictory)
1: Set an allowance, and except for special occasions, don’t buy anything else.
2: Take child to the store, and show them how much toys cost compared to food, etc. Many children (and adults) have no concept of Cost.
3: Take your child to a soup kitchen, Tomchei Shabbos, etc (assuming they are old enough to understand) to show them how the “other side” lives.
4: Work on delayed gratification. Tell you child “you can have it, but then when you want a bigger present (birthday, etc.) you will not be able to get one. AND FOLLOW THROUGH!
5: Start a savings account for the child, and show how small amounts add up when saved over long periods.
Good luck, and feel free to add or argue.