Every person is uniqu. You cannot judge the necessities and interests of other person. There is no objectivity in priorities.
In India, children and women are not economically independent for long span of their life. That gives control to the person who is earning. Even earning children and women are emotionally dependent on parents. So they themselves handover their income to elders on the name of respect.
In general, people, especially parents judge the priorities. Parents give money to children after making judgement. They evaluate the necessity of thing that has to be bought. There are few psychological issues related to this. Parents negative comments before allowing children to buy can generate guilt in the children.
Alternative solution is to teach responsibility. Parents can teach children how to spend money. Choice of what to buy has to be left to child. Instead of making analysis before buying, general discussion could be carried out in order to understand interests of others. During discussions, children will understand advantages and disadvantes of materials. They also might get new perspectives regarding necessity.