Adults think we know what is best for children. We have responsibility for them – feeding them, clothing them, educating them, protecting them, loving them – but we also assume rights over them, and on their behalf. Adults make rules (including laws and policies) about what children can and cannot do. We expect children to behave according to our rules.
It’s also the case that when researchers are trying to better understand children’s needs and well-being, we usually do not ask the children themselves. Instead, we ask their parents or adult relatives, or their teachers, for evaluations.
There are good reasons why survey teams do not talk to children, even older children who have a strong understanding of questions, starting about age 10-12. Children are considered vulnerable because they are dependent on the adults in their lives. If an adult heard a child talking to a researcher, perhaps saying something the adult did not like, the child could be punished.