https://en.wikipedia.org/wiki/Operation_Babylift

The answer is more complicated. These were children from the Democratic south which was allied or puppeted by the US. So their parents were more likely killed by the North Vietnamese.

The bigger issue is many of these children were not even orphans and were placed in orphanages due to poverty. Many had living relatives that intended to take custody after the war.

And of course the modern Vietnamese government opposed the action as they were the winners of the war. I'm really struggling to find the sources on if the South Vietnamese government had an opinion, although at this point it was probably whatever the USA says.

Cold war proxy wars were a fucked period for sure.