The sexism comes in where the women are given an infinitely harder time in order to make partner (not "one of the boys" so invariably work twice as hard for same recognition, not "made in the same mould" so find tend not to have a natural mentor who "sponsors" them through the process). Male partners in my firm often work from home to see their children/assist with a childcare issue and arrange their diaries around family-related activities (good - it's the 21st century!)
I've seen this at first hand, and you are right re women but you don't quite describe the dynamics with the men. Firstly, the men won't exhibit much "Daddy" behaviour while shooting for partner (the opposite in fact), that only comes once through the gate and with feet comfortably under a table. Secondly, there is discrimination within the men as well, those whose faces don't fit can also forget making partner.
Big picture, the City is better for women now than it was 20 years ago, but the crunch point still comes when children arrive. Any sign that you are not fully committed to the cause (and going part time is the kiss of death) puts you on the Mommy Track (and Daddy Track btw, it happens to men as well). Women are better off trying to shoot for partner before having kids.
The City is not sexist these days IMO so much as workist - it wants those who will marry it, not another person.
IMO the biggest issue for Feminsm today (in the UK anyway) is to deal with the discrimination when kids arrive, and that is largely due to the high complexity/cost of finding childare that covers the whole working/commuting day.
I think its absolutely no surprise that ambitious, clever women are the major forces driving small business creation and the move to professionals working from home businesses.