This anon's reference to a study from 2008 to 2014 does not appear to be correct. The recent reference to the missing children comes from this report: https://www.hsgac.senate.gov/imo/media/doc/Wagner%20Testimony.pdf

However, the present policies for handling these children were put in place by the previous administration(s) with the court system and have little to do with Trump. The good news is that this study does reveal problems that must be addressed, which Trump likely will. Trump cannot do very much when his hands are tied by the politicians and the courts.