[citation needed] - were the Republicans complaining about this at the time?

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.