Good grief. Where they are coming from, the gang violence makes it a defacto war zone. They can't go back. Under Trump, the legal apparatus for coming through the ports of entry was hamstrung - on purpose. Trump didn't want to just stop illegal immigration. He wanted to stop legal immigration. So, he dismantled part of it to make it harder on people trying to do the right thing. So, those people ended up being told to wait. For years, sometimes, on the Mexico side of the border. Without any place to stay, or work, etc.
Biden asked the Trump administration to increase funding for dealing with unaccompanied minors, and to start the upgrade process on their facilities. Trump did not even begin the process until the day before he left office, just so he could claim to have done it, and Biden would be stuck with as long a wait as possible to implement changes.
That is the epitome of jerkishness right there.
So, the predictable outcome of the Trump policies was more people attempting illegal crossings, because there was simply no viable way to cross legally. The other predictable outcome was that there would be more children than could be safely handled by the system. Trump ensured that this would happen.
Biden is ramping up changes as quickly as possible, but he is literally having to do everything with constant opposition from land mines left behind by the Trump administration and the Republicans in Congress refusing to do anything bipartisan.