A couple of points:
tax is not just direct tax on income. Tax also comes in the way of cost of items from food to fuel and from alcohol to sugar and from energy to sanitary towels. You can't just look at how much tax we pay on our salaries/income and how much people in other countries pay. You need to look at that plus cost of living, inheritance tax, the cost of buying and selling homes, etc. Just comparing direct taxes will give you the wrong picture.
Childless people do not get anything comparable to childcare allowance or anything relating to children 'benefits.' Yet they still pay the same amount of tax as people with children. That's the unfairness. The NHS, etc, doesn't count - because it's not something childless people get but people with children don't. If you don't get this point, nobody can help you understand it.
People have children because they want children. Not because they are concerned about who will look after people when they are old, who will drive buses, etc. If they didn't want kids they wouldn't have them. They are instead having them because they want to be parents, have a family, etc.
Today's kids will indeed pay for our pensions, the services we will use, etc, when we are old. But that is neither here nor there as we are currently paying those things for today's pensioners. So we will not get anything we have not already paid for.
The government further subsidising childcare when there are many other services, of greater benefit to a much greater section of the population is, frankly, risible. Lots of people save and plan before having children in order to be able to afford whatever they want for their future children. Having kids is not a right, and certainly not one anyone should enjoy at other people's expense (literally).