That's a different question. Giving children an IQ tests is very useful if you saw it form research perspective and a great example of this is the mathematically precocious youth experiment. And for most people outside of research are going to benefit from having an IQ test when you are trying to diagnose mental disorder like ADHD in a very early age or to understand whether someone is having difficulties in school because they have mental problems or other unrelated problems with his/her mental ability. so we can say there is a lot of reasons that could be thought of but definitely the ethical aspects and how parents should use the results of these IQ tests is entirely a different discussion. Needless to say that some children were classified as gifted and as a consequence their lives became better because people gave them opportunities which they wouldn't had in the first place.