If you're comparing Xianjiang and what's happening at the border then this is not eve remotely 'equal opportunity' criticism - it's classical Chinese moral relativism.
In Xianjiang people are being rounded up for their religion or ethnicity, thrown into concentration camps, made 'non-persons', tortured, killed, if they die on trumped up charges their organs are harvested. It's Nazi-Germany level stuff.
The US is not 'putting children in prison' - the US (was previously) holding people who are trying to enter the country due literally to the prosperity of the nation. They are well treated and are free to leave any time.
Now that the rule has been discarded, migrants bring their children specifically on the dangerous journey because they know if they bring their kids, they don't have to go into detention.
This year there there has been a massive upswing in illegal migration precisely because migrants now know the golden legal loophole: bring a child - and they won't have to be held, they can immediately enter the country. And of course, the irony of the fact these people are desperately trying to get in to the country should not be lost on anyone making morally relative claims comparing that situation to Xianjiang.