Federal law prohibits discrimination based on status as a parent. Your company cannot exclude a job applicant from the pool of candidates because “she’s got kids and will probably need more time off.”
Federal law also prohibits discrimination based on pregnancy. Your company cannot treat a female applicant or employee unfavorably or unequally because of pregnancy, childbirth, or related medical conditions.
Your company also should not discriminate against a woman because you believe that she might be pregnant or likely to be pregnant (suppositions based on age, marital status, or other information volunteered during an interview).
Questions about number of children / dependents and marital status are often necessary for completing paperwork, including tax forms, retirement plans, and medical insurance plans. These questions should be kept separate from the hiring process- you should not encounter these questions in an interview; you may provide the information on the necessary forms after the hiring decision has been made.