Frankly I'm surprised having children these days is even happening. In the past, you lived close to your job, you could afford to have one parent at home or you might be able to hire a housekeeper or a nanny, you lived close to your kin, you could kick your kids outside in the morning and call them back in the evening.
Our modern world is not really tailored to having kids. No financial incentive really addresses this. For example...
Having a decent standard of life and the amenities most people want to give their children often requires both parents to work. And if you work, you probably live some distance away from both your job and the daycare, and so the the daily dash to take your kids to daycare and get them home before the daycare closes, plus the commute to and from work, is a stressful race you need to run every fucking day. Having to drag your tired, hungry toddler with you to the supermarket to do your grocery shopping is harrowing. Leave your kids in the car as you used to do in the 80's? Lol nope, someone's gonna report you, you bad parent!
Even our best cities are not walkable or safe for kids, so you can't let them out by themselves or someone's gonna report you. Communities are fragmented so your friends, colleagues and relatives live far away, so most of the time the responsibility for the kid is solely on parents, whose time is stretched thin as it is, and is going to get strected even thinner as more and more societies expect adult children to care for their elderly parents as well.
So kids are a lot of daily stress even before we even address how vexing small children can be by themselves. And contrary to the past, parents don't get any material benefit from having kids. We don't need their labour at the farm or in the family business (and indeed child labour is rightly frowned on these days), we can't count on the kids to support us on our old age since they probably need to move away for work anyway. Reading the news about rising graduate unemployment, it even seems like we don't have much use for those kids even after we put them through years of expensive schooling.
So why do it? You need to be fucking dedicated to the idea of having children if you still take the plunge. Parents, I salute you, but I'm not surprised more and more people are opting out.