https://en.wikipedia.org/wiki/Internment points out that internment "is the imprisonment of people, commonly in large groups, without charges or intent to file charges, and thus no trial. ... Interned persons may be held in prisons or in facilities known as internment camps, also known as concentration camps."
It then quotes The American Heritage Dictionary's definition of concentration camp as: "A camp where persons are confined, usually without hearings and typically under harsh conditions, often as a result of their membership in a group which the government has identified as dangerous or undesirable."
Ergo, prisons which only contain people who have been convicted in a trial or agreed to a plea bargain cannot be regarded as concentration camps.
By comparison, the US held Japanese Americans in concentration camps during WWII, and held Filipino civilians in concentration camps ("reconcentrados") during the Philippine–American War. These can be distinguished from prisons as there was no trial for those held.
As I understand it, if the people being held at ICE are asylum seekers, then entry into the US is not illegal (even if they are not granted asylum). The US instead argues that they can be detained until that process is finished, even if that is indefinite.
This certainly sounds a lot closer to the definition of a concentration camp than US prisons containing prisoners who have be convicted in a court process.
In any case, we're talking about people in an organization which argued that the requirement for "safe and sanitary" conditions was so vague that it was okay to refuse toothbrushes, soap or adequate bedding to children.
Are all US juvenile prisons the same way? No. The 'typically under harsh conditions' is yet another distinction between "concentration camp" and "prison".
That said, many US jails and prisons are horrid, inhumane places.
"No one truly knows a nation until one has been inside its jails. A nation should not be judged by how it treats its highest citizens but its lowest ones." - Nelson Mandela in Long Walk to Freedom.