Glad you reached a decision you are happy with, Weasel.
I guess the decision you reach for many women will depend on whether they take a long term or short term view.
I suspect most SAHMs take a short term view, and stay at home whilst their children are young, noting that the money does not adequately cover the costs of work.
However, I suspect most working mums (myself included) take a more long term view, noting that whilst I didn't make much money whilst my DDs were young, once they got to three the 15 hours childcare really helps to minimise my costs now (I work 5 mornings, but only pay for two), and of course, I have managed over the past 5 years to work my job round the school day, so when my youngest starts school next year I will be able to pick them up from school every day and work are more amenable to my demands for school friendly hours, because I've done my 5 years of compromise and have proved my worth. I would not get such child friendly hours in a new job, and indeed it has taken me years to really get good hours. So I balanced out 3 years of working part time, and my DD going to childcare part time Vs the next 15 years of being there to pick my DDs up from school and being able to pick my children up from school, and having a job where I largely work school hours.
Financially, for me it didn't make sense - but logically, the benefits have!