Tangentially related Q: in the USA there are “illegal” immigrants who have moved into the country. I worry about human rights abuses against these people. What are the methods available for these people to become citizens if they so wish?
However, they often are not eligible to do so because of their illegal prescence. If one has been in the US illegally, as an adult, for more than 180 days, they have a three-year ban. After one year it becomes a 10-year ban. This applies to both visiting and immigration. They have to return home (or another country) to serve the ban before getting a visa to return.
One notable exception to this rule is marrying a US citizen, but only if the initial entry was legal (i.e. visa overstay, not border jumping). Being a parent of a US citizen also works, but the child has to be 21 first. Being a parent of a US citizen under 21 has no immigration benefits.