People losing their minds over this would sound a lot more sincere and principled if they'd been even half as upset about Obama placing kids in actual cages with a much higher per capita death rate. Now they just sound like ideologues grinding a political axe.
The policy before Trump was to hold children who arrive unaccompanied at the border and find their family to reunite them with. The policy under Trump is a zero-tolerance separate all children from their parents policy. Trump HHS currently cannot account for around 6000 children they have separated. This is new. The new rules around immigration seem to be focused around overwhelming the system's capacity for processing people fairly and with proper oversight.
Obama's immigration policies were criticised by liberals (as were many other aspects of his presidency, or are we going to rewrite history to state that OWS was just a public Obama fan-club gathering?). They were even outed by left-leaning publications and subject to a documentary on PBS.
Back on the topic of the comment you shifted away from - "deporting" in US-speak means sending people to a private prison where detainees are effectively forced to work, but without even allowing the accused their fair time in court. At some point after that they might get sent back to another country.
If you call them concentration camps, if you call them private prisons, if you call them anything besides detention facilities, you likely haven't thought about it much, because only a detention center will allow you to sign up to be let go back at the border. "Hey, I've decided this sucks, I'd like to head back home," is something you only say when being processed at the border in a queue.
Are you actually free to say "Hey, I've decided this sucks, I'd like to head back home?" My understanding is that they aren't, and that to leave the detention center, they need to have their application for "voluntary departure" approved by an immigration judge and pay for their own transportation out of the country:
But maybe that's just my differing opinion.