How to be fair when giving pocket money to children?

Fairness in this matter should be in the form of MEETING THE NEED. For example, giving pocket money to a child in university is not the same as giving pocket money to a child in primary education. We are fair by looking at the need, not the numbers. Another example would be the difference in the needs of boys and girls. We can multiply these examples; In all of them, the result will be meeting the needs.