The only assumption I'm making is that P(absent|women with children) >> P(absent|no children or man). Do you dispute this prior? Similarly, you might also (unlawfully) ask about potential military service obligations if a person listed "Army Reserve" on their resume. Would that necessarily be motivated by anti-military bias? Of course not; it could simply reflect a desire that employees predictably show up to work. (As pointed out downthread, illegal != sexist.)
Note that I didn't say anyone was or was not sexist; I simply said they might not be.