Obama made changes to the Flores act which started due to a girl being strip searched. Obama separated the children by law for their protection from sexual abuse. The addition he made was to make sure the children were held in those conditions for no longer than 20 days. This was done to maximize the number of “anchors” released into the interior. Once inside, they were allowed to bring over their entire family through chain migration.

The vast majority of children “separated” were literally brought over by people who weren’t their parents or they were unaccompanied entirely. Preventing them from being trafficked by separating them wasn’t working so trump enacted an order to keep all immigrants in Mexico until their court date. This almost entirely stopped the use of children to get into the USA as they weren’t able to chain migrate. Trump literally exposed the system and stopped it. Biden signed away the trump EO on day one and the traffickers started using children to game the system on day 2. He literally brought back the cages and the entire clusterfuck of immigration policies that allowed children to be used to break into the country.

The highest number of unaccompanied minors was just 2600 under trump. Today, under Biden the number is over 16,000 and growing rapidly.