How can the study of children each ine unique be a science?

The study of children, each one unique, can be a science by itself because there are plenty of scientists, even physichologists that build hypothesis and conclusions using children as object of experiments. Based on how will they react, depending in each stage of their life, is a concern mainly when there is an especific mental or behavioural disorder. So they are unique in science because they are imperative to obtain results, data or conclusions.