I think its all a game we play and we make decisions accordingly. Those that need to work make different decisions to those that stay at home.
I work, need to work and so decided to have my two children three years apart. This means that when I went back to work after having DD2, DD1 was getting her nursery childcare fees paid, so that accounted for 12 hours of childcare. Only having to pay for one child at a time makes it affordable.
Also, those of us that work when they're young I think tend to it for the long term gains. I'm a teacher too (FE) and by working, I am now able to work mornings, so that now my DDs are at school, I am able to pick them up every day. If I had been at home, I would not have been able to have the hours I have now and I would now be paying childcare.
Also, over the years I have been working, my wage has been rising and I would not be on the same scale as I am now if I had taken the time out. (I would be earning 8k a year less if I went to my place of work now).
And of course, there's pensions...
Yes I could have said once the childcare had been paid, I wasn't left with much - but that would have been very short sighted of me. Instead I looked at the long term gain, and I find having a term time, school hours only job that pays well and is a rewarding career in its own right is more than worth the salary sacrifice I made in the early years.