Initially, people crossing the border illegally.
Correct -- with their children, who presumably had no say in the matter and are thus, innocent of any wrongdoing. Punishing children for their parents' actions may be Biblical, but it's not how we do things here in the U.S. of A.
Now, one may very well say, "Aha! But they're still in the country
now benefiting from their parents' illegal acts!" Which is a valid point, but consider:
Two parents, let's call them Joe and Mary, commit a crime -- they rob a bank.
Why would they do such a thing? Turns out their 4-year-old son -- let's call him Jack -- is very sick. He needs a kidney transplant, Joe and Mary have no insurance.... etc., etc... I'm sure you've heard the story before.
Well, the bank heist goes off without a hitch, and Joe and Mary use their ill-gotten loot to pay for little Jack's new kidney... but the case remains open.
Sure enough, eighteen months after the robbery (and a year after the surgery), the police catch a break in the investigation, and Joe and Mary are caught.
They're going to prison (as criminals should), and little Jack's heading for a foster home (tragic, but unavoidable)...
"There's just one more thing..." the judge says after passing sentence, "...we're going to need that kidney back. You see, since it was paid for with stolen money..."
Fair or unfair?