Children are future taxpayers the majority with parents who were not a tax burden --net positive tax contribution. People without Children benefit from the taxes paid by the children of people who rear children -i.e. people without children aren't "cashing out" their tax contributed retirement --that contribution went to other retirees.
The vast majority of adults and their children will never pay their tax burden proportionately.
Immigrants pay social security taxes, unemployment taxes, ... that they also will never be able to benefit from. Those are purely for the benefit of US citizens
And citizens benefit from the taxes paid by non-citizen immigrants, whether documented or undocumented. Not just income and payroll taxes that might be dodged by under-the-table arrangements, but sales taxes, property taxes (perhaps paid indirectly via rent to a taxpaying landlord), the consumer share (nearly 100%) of tariffs, etc. And much of that tax base is spent on benefits and services that are not accessible to taxpaying non-citizens.
So from that standpoint, immigrants are a /better/ economic deal for the public than children are. At the end of the day, though, it shouldn't matter where people were born if they're contributing to society, and the grandparent post is 100% correct that the whole debate is stupid.