The correct answer is: "Parents must be notified that the study is taking place."
According to the American Association of Public opinion Research (AAPOR), in order to perform the survey, a researcher must get the approval of the parents of the children who are going to surveyed. However, even if a researcher gets the permission from the parents, federal regulations require that children express their agreement to participate in the survey. Factors like age, maturity, and psychological state need to be taken into account at the moment of asking for their consent to participate.