i'm going to post & run, i'd afraid, as dd about to get home from school, but WHY are you all looking at how much of the woman's income is left over after paying for childcare?
does the father not contribute AT ALL?
surely you look at family income - childcare = ?? to see if both parents working is worth it?
are you all saying that the woman earns less than the man even before the first child is born, in every instance ? (in which case, there's a lot more to worry about than the cost of childcare)
you also need to look at pensions, co. benefits etc, and associated costs (e.g. travel to work, 2nd car) to get a 'true' picture.
then factor in the long-term effect of not working for several years, starting again at a lower salary etc.
that gives you the financial picture.
THEN you get to consider quality of life.
It's a tough decision either way, but JUST looking at mum's salary - childcare costs is totally inaccurate & hugely misleading.