Fucking hell, here I was thinking mumsnet was a forum of generally intelligent posters and came across this thread where people live in a reality where income tax, student loans, travel expenses, and shared finances don't exist. OP you're a saint for dealing with some of these morons.
I currently have a child in nursery so know exactly what you're going through. It's definitely motivated me to go for promotions/pay rises as otherwise it's mentally hard to leave my daughter for others to care for if the household won't financially benefit in the short term.
However, main motivating factors for returning to work were: financial independence (I love my husband but I've seen too many women screwed over by divorce to risk relying on him), career progression, pension, maintaining skills (I already lost so much confidence with my 6 month mat leave, I don't know how I'd manage after years out!).
It does help to think about how short this time period really is - once your eldest goes to school you'll be a bit better off financially even with wrap around care.
YANBU to think something is wrong with a system in which you're earning well over the national average, have only 2 children and still not taking home any real net profit.
Other countries manage to provide affordable childcare, the UK chooses not to. The public are so defeated that they'd prefer to call working mums unreasonable for expecting some financial compensation for the hours they put in rather than protest the government. Meanwhile the government scratches its head and bemoans low productivity.
If we had childcare as a tax write off or treated it like a business expense I'd wager we'd actually boost the net tax margin, raise productivity and lower the amount spent on benefits. Why make women either struggle or opt out of the workplace for up to 5 years when we could enable them to work the hours they want to?