Presumably you would have to obtain an estimate of this yourself, perhaps by surveying the students (i.e. taking a sample, and using that to estimate the proportion of all students that are parents).
You would have to carefully consider how to obtain this sample though, in order for it to be balanced (be a non-biased reflection of the whole student body). So, you might survey students at random from each class, across different times of day, making sure to have a mix of ages, gender, majors etc. in your sample that is close to the overall mix for the student body.
If your sample still ends up looking different to the population (e.g. you end up with more female than male respondents, but the overall student body has an equal mix) then you might also consider weighting each response based on these demographics - make each male response count a little "more" and each female response count a little "less" to match the overall male/female split in the population.
Hope this helped!
Content will be erased after question is completed.