However I suspect that in the case of a US citizen, that doesn't mean you don't have to officially declare your tax status/income to the IRS each year. Hence the parents worry that he's going to have to trawl back over his entire working life to 'prove' that he doesn't owe any back taxes.
IANAL, but am from the UK, lived in the US for a few years and have had to deal with moving back and forth.
However I suspect that in the case of a US citizen, that doesn't mean you don't have to officially declare your tax status/income to the IRS each year. Hence the parents worry that he's going to have to trawl back over his entire working life to 'prove' that he doesn't owe any back taxes.
IANAL, but am from the UK, lived in the US for a few years and have had to deal with moving back and forth.