Learn to Recognize the Difference
There are people on the interviewing panel who would like to put you at ease with small talk. These people would ask you questions pertaining to your family, hobbies and other 'small talk' stuff without realizing that they are asking you unlawful questions. In such cases, most of the candidates would prefer to step aside diplomatically rather than "fight for their rights" so they would still have a chance to get the job.
When the questions are innocently put, redirect the same question to them. Say, when they ask whether you have children you can always say, "I guess you love children. Tell me about yours." This should give the interviewer a heads-up regarding the faux pas. If not, you could state in a calm and neutral tone, "I do not understand your question, as I am aware that my having children, marital status, or age is not imperative for this job." This should make it clear enough.
There are times however, when the interviewer does cross the line. At such time, you could point that such a question is not legally correct and say, "I would rather not answer this question."
What are the Questions?
Some of the questions which the interviewers should not ask you are listed below. The list is long and if you need more information you can always take a look at the US Equal Employment Opportunity Commission - http://www.eeoc.gov/employees/charge.cfm .
- Age Questions - The interviewer should not ask any question that leads to finding out your age, or how long you have until retirement. However, they can ask about your plans for furthering your career.
- Family Details - Any question relating to your marital status, plans about having children, your maiden name, etc. are off limits. Redirect the questions to whether or not you could put in long hours of work, extra time, travel time - if that pertains to the job.
- Religion and Beliefs - The interviewer cannot ask you about your beliefs, religion, or ask you what religious holidays you observe. You could redirect the question by finding out whether they need you to work on any particular days or period in the year.