Court TV's Legal Cafe (
http://www.courttv.com/archive/legalcafe/work/hired/hired_background.html)
According to state and federal laws, prospective employers generally must limit their inquiries to topics that explore your qualifications for the job. Any questions that probe for personal information that can be used to discriminate against you are no-nos. Not that it stops some prospective employers from trying to decipher the information more indirectly. A seemingly friendly question about your name ("Gee, Kotzamani, that's interesting. Where's your family from?") is not so friendly if the interviewer is really trying to scope out your race or nationality.
The specific topics you cannot be asked about in a job interview include:
your age
your sexual preference
your national origin
your race
your religion
your medical history
Potential employers are allowed to inquire whether you're married and the ages of your children--so long as they ask every potential employee the same thing--and don't base their hiring decisions on the answer. If, however, only female job candidates are being asked their marital status, and if the company is not hiring any candidates with children under age five, then what is a totally legal question may be suspect.
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Obviously, the questions about religion are forbidden ground. The question about children is probably a gray area. However, since they are asking the age of the children, my worry would be that they are trying to wean out applicants who have young children (because young children generally require more of mum or dad's time and can take them away from the job more).
Personally, I would forward a copy of the application to your state labor board.