I would never ever pursue a relationship with someone who has three children with three different people, and yes, that applies equally if we were talking about a woman with three kids with three different fathers.
Making what seems to be a good decision to have a child with someone who seems to be a decent person but who then turns out to be awful, is the sort of thing that could happen once to an intelligent person. Three times? Sorry, but the person is probably a flake who makes poor decisions in life and/or is the cause of problems in their relationships due to being hard to live with and hard to get on with.
Also, if you have two kids with two different people, that is your cue to “focus your time and energy on raising properly the two kids you have already got,” not to spend time and energy pursuing new relationships and making more kids, and further complicating things for the kids you already have and who already have quite a bit of complication to deal with.
I’m not sure why “Kate Winslett and Madonna” are considered to constitute some sort of compelling counter-argument? Hollywood stars are mostly flakes and the worst relationship material in the world, as their extremely high rates of relationship breakup suggests, so no I bloody well would not date either of them if I was into women. (Also, last time I checked Madonna was putting photographs of her arsehole all over the media, so maybe not the stable person in general.)