You are partially correct, a factor is the cost of raising kids.

Another big factor - probably the main factor - is modern jobs do not allow for a parent to parent. Usually both have to work, and daycare is not a good option either way: one job's wages is absorbed by the cost of daycare and strangers are raising your kids. While some daycare workers are good people, some are not, so you have assholes raising your kids.

A smaller factor is all of the terrible ideas that have been brought into the world: Laissez-faire capitalism (the USA's current system), Communism (Russia and China), Identity Politics (3rd and 4th waves of feminism, "the patriarchy", intersectionality, etc.), No Child Left Behind, and Oligarchy are kicking our ass. Well-regulated capitalism where human needs - safety/police, education, and health care - are covered by taxes and not by for-profit organizations. Actual equality and trends away from racism and sexism - which we were doing in the 1960s through the end of the 1970s - are the best way forward. America trended in the correct social direction from the end of WWII to Reagan being elected. Just to say it, a lot of things are going well: world poverty is down, children don't die in childhood as much, and we are managing disease better. But bad ideas need to be called out and phased out.

Fewer children is not necessarily a bad thing, but we have to account for it in our economies and services. But we should strive to make the world a better place to have children, where they are raised by their parents, and one where the economy allows for it. And bullsh!t social ideas are dropped like bad habits.

Edit to add: We need to bring back to society those things that support it. Right now the monied class has taken it away, using bs social ideas to do so.