^Every parent has a choice . There is a choice where you live. If you choose to live in London costs are going to be higher.
Alternatively, stay at home, invest your time in your own children caring for them yourself. Stop complaing . Childcare shouldn't be cheep .^
There is not much point in delving into this but it is common knowledge that it is not just as simple as moving out of London, or anywhere for that matter, especially if your work and/or accommodation are rooted where you are now. Plus London is not meant to be a child-free zone and it is not supposed to reserved solely for wealthy families.
Additionally "investing your time" may not make sense for many. Let's say a couple both earn £25k and take home c. £20k each. Their annual childcare costs are c. £10k (using an estimate based on quoted childcare costs upthread). So they take home £10k less than they did pre-DC, but if one stayed home or they both went PT to have a parent at home every day then they would be (very roughly) £20k down. It's highly likely that it wouldn't be feasible to do that. They also may only be able to afford to stay home by receiving benefits, if as a household they would be eligible (which I think they would be entitled to some with a household income of £25k pre-tax), which the government doesn't exactly want to encourage.
No one is saying childcare should be cheap. Just that it should be reasonable when it is in the interests of many for parents to be able to work full time. As I said upthread, if you have 2 parents in work that are paying for childcare, there are roughly 3 wages being paid which means 3 lots of tax, NI, 3 people in employment and therefore not wholly (or possibly not at all) dependent on state benefits, 3 lots of income that can then contribute in the form of purchases, plus 3 people who are maintaining and developing skills and potentially have routes for progression, and so on. It is therefore in the wider interest for parents to be able to both work and afford childcare. The alternative is not wrong and if people want to stay at home then that is just as valid, but if people are staying at home because they feel that they can't work - or even, childcare costs would meet or exceed their wage and therefore not be sustainable for their family - then that just doesn't make sense.
The opportunity to work and pay for childcare shouldn't be treated like some sort of luxury, and the decision to have a child shouldn't be treated as merely a luxury either. It is quite common to want to have a child and many parents struggling with childcare costs are people with decent salaries, it would be hard for many to reach a point where childcare becomes a comfortable expenditure in time to actually have children.