I don't know if its morally correct to ask these types of questions to students whose age falls within the lower end of the study (i.e kids between the age of 12-14 years), since that is the beginning of adolescence, where sex drive is just starting. The same reasons as to why sexual education isn't usually discussed or taught in schools until approx. age 14 can be associated with the reasons as to why students that young should not be included.
Obviously, the concern about anonymity is a high priority. The reason being is that if this information was ever released, it may have a big impact on that person's life and self-esteem.