What sort of world did a child born in Europe in 1900 or 1930 inherit? What about a black child born in the US in 1950, or South Africa in 1960? What about a child born in China in 1950 or (what is now) Bangladesh in 1960 or Sri Lanka in 1970? Their children and grand children will have a much better life.
Like, I certainly cannot afford a family of 12 children. Nor can I afford to buy the amount of land that they acquired, and certainly not by working the same kind of jobs they did.
But usually the "requirements" that get parents to spend too much money are entirely optional things, of which a few are college tuition, a car for the child, camps, tutors, music lessons, vacations abroad, innumerable toys, iPads, etc etc
The median household income is under $80k, while median yearly housing cost is around $25k, food expenses for a family of 4 are $12k-$19k, median utility costs around $4k, health insurance $27k (about to go up), and median cost of vehicle ownership is $12k. Yearly figures. That’s sharing one car between both working parents and we’re using median numbers here, and the median person doesn’t live in a place with great public transit options. Already that leaves almost nothing to deal with emergencies, saving in case a parent loses their job, and miscellaneous expenses like school books/supplies and clothing. And perhaps contributing to elder care for 1-4 grandparents.
Also, this is just the median; people in the lower 50% are much worse off, except for those poor enough to receive substantial aid. And don’t forget that young people typically have lower incomes.
You really don’t want half of your society to decide that pets are cheaper, unless you want to end up with an inverted population pyramid and eventual collapse, or unlimited migration to replace lost workers (which creates its own problems).
This is not the 1940s:
Cheap homes are unavailable. Even single family homes are becoming unaffordable except in isolated areas without jobs. Housing costs, even apartments, have gone up enormously as a percentage of income and building/health codes don’t allow you to live in shanties.
You need a phone now for most jobs. People aren’t hiring you if you can’t be contacted except for bottom of the barrel work. You likely need internet if your job requires remote work and kids probably need it for homework.
People in the mid 1900s had single earner households and households or neighborhoods with extended family. That means more time for cooking, sewing and repairing clothes, and other housework. Work often wasn’t as far away, especially in working class neighborhoods, so you might not even need a car.
Besides all this, literally nobody is going to have kids if it requires going back to a 1940s standard of living. That’s society’s problem, if as an aggregate entity it cares about perpetuating itself. If nobody cares, fine, let it fall apart.
Median people in the USA eat extremely lavishly. Your series of comments, to me, boils down to a complaint that you can't maintain this extreme luxury while having children. Yeah, nobody ever could. The time frame in which people were "able" to have a lot of children was the time when they weren't living such extravagant lives of consumption. So yeah if the complaint is "Why can't I afford a lifestyle that would make my grandparents blush with shame at its luxury, and have as many kids as them, wtf?!" then I'm not very sympathetic to it.
If everything goes alright for them. The thing is that we don't know about knock-on effects and monkey paw results - we can switch this gene on, your child has IQ 190, but later parents will figure out that it has social intelligence of a rock. Or we can switch this gene on, your child is now able to compete with marathon runners, whoops heart attack at 32 years.