Is It Normal For A Child To Have Cylindrical Power In Both Eyes And Needing Spectacles For Perfect Vision?

Hi Sir, my 6 years old daughter has -3.5 cylindrical power in both eyes at 170 axis. Doctor suggested to wear glasses. Why she has this problem from this age? She is not watching mobile more time. Is it necessary wear glasses continuously? Or can she wear it at the time of school and tv time? Please suggest