You say 'survived' that is very different from 'living'.
I am pretty sure most of us can 'survive' on much less than we do, we can all do without new clothes, nights out, make up, streaming services, mobile phones, bottle of wine on a friday etc etc but most people don't want to have to scrape by!
Of course there are sacrifices to be made when choosing to have children but most people do want to provide there children with a certain level of luxury and are entitled to that opinion.
People also have different levels of out goings - council tax varies - ours is £218, back in 2019 it was about £190 which would use up nearly half of your £400 that you had to live off. add in electric, gas and water and we would then have NO money left for food, school uniform, internet, TV, mobile phones, medicine, toiletries, petrol, car tax, car iinsurance, house insurance, buildings insurance, life insurance, kids activities, school dinner money and so on and on. I really dont believe you were living a nice life on £400 unless you mean after all your bills had been paid??