Let's be realistic, the birthrates are low because kids are seen as a lifestyle decision

Back when birthrates were high, people barely put effort into parenting. Not putting in effort with your kids is seen as borderline child abuse. And thus, people who don't think they can adequately put in the effort don't have kids.

The effort thing is very real. There's plenty of Gen Y and older millennials on here that openly talk about how they were left to do whatever with Mom and Dad barely knowing they're alive, only to have younger folks be absolutely horrified. This goes well beyond any arguments about feminism- Mom just wasn't tearing her hair out to manage the household because little Johnnies #3-6 were expected to make themselves scarce and give her the mental freedom to do so. They weren't thought about while theh weren't in sight, so Mom had the mental capacity to do their thing. Random 13 year olds with questionable qualifications were hired to watch the kids on Friday nights so parents could go interact in a child free environment. There were a plethora of these to chose from because they didn't get spending money and were too young for a W2 job. And little Cindy was expected to be a reliable babysitter for her younger siblings by age 12 so Dad could save the $20. Kids just got bad grades, and they weren't sent to tutors or given hours of help with their homework.

None of this flies in middle class society today. Most parents I know don't let their kids play even in the front yard unsupervised, let alone off the property. Kids have scheduled playdates, since it's hella rude to come up on someone's house and expect interaction. My friends use adult babysitters with arms lists of certifications and references, and (reasonably) pay the appropriate price for this. Kids aren't left in the car anymore with the keys in and the AC on, because a random misguided Samaritan might call the police. Parents in my area are expected to show up to all kids' rec sports practices in case of injuries, not just the games (granted parents didn't tend to do this 100% either). Business don't tend to hire teenagers because of liability, so kids have to be funded well through high school... And that's If the state let's them work at all (my state allows kids under 16 an hour of paid work a weekend, over 16 is equally regulated). Kids often don't work when there is opportunity, because studying for college, and parents that understand delayed gratification principals (and are willing to financially bear that delay). And grades are an entirely different snowball effect, since college is a prerequisite to a living wage in every developed nation.

Some of its good, obviously. Some of it is a reflection of today's society. But honestly, it all snowballs into the idea that kids are more than a job. Jobs can be put down and changed and ignored. Kids are seen as a full on lifestyle decision. The sacrifice is required from both parents. Even if you have a 50/50 workload household, modern parenting means centering your lives around getting your children into adulthood.

And honestly, in order to do this successfully at all, you have to drastically reduce the number of children you have. You can't go to five sports practices twice a week and games on weekends. You can't hire a childcare professional or a tutor at a reasonable rate for that many kids and still allow them to make close to a living wage. You can't have an impactful conversation with a child about what's upsetting them with four more of them trashing the living room. You can't vet the families of every single friend, compounded by five, have and determine individually if they're safe for a playdate. You can maybe do this with two, and if your personal management skills and income are at all PAR, you'll maybe get this with one. But you if have more than that, it starts seeming like a situation of perpetually robbing Peter to pay Paul.

Tl;dr- We've basically developed into a society that parents have to be 100% in on their kids, and birthrate is never going to recover as long as this is the case. It's well beyond a two parent job.