In some ways, I disagree. I've found the expenses of children to be bathtub shaped - very expensive up front, dropping until they start public school, then ramping up slowly until they make the big jump to college.
So those are some ways. Paying for phone plans (my parents didn't) could also get expensive, as could clothes if they don't have to buy their own.
Progressive Era reforms mean it’s harder to get them to make money, but they are still expected to “volunteer” in community organizations. Many high schools require “volunteer hours” to graduate, which means you drive them to their job where they make no money and then they quit once they accumulate the mandated hours. Working in one of these community organizations, I found it pretty annoying.