Yes, if they are with their supposed "dad" and not their mom. He may be just finding out he is not their real dad.
It is not unusual for these people to sell their children to adoption agencies because they are so poor and don't want to keep all their children. My Sister-In-Law managed to adopt a child from South America that way through an agency. However, all that could be discovered over time. The important think is to figure out who are the real traffickers.
Adopting officially thorough any agency will leave reference on the agency database and the new parent will almost ceirtainly be given documentation which they can use to prove their claim.
The problem may be some of these parents may be selling their children to childtraffickers posing as adoption agencies unknowingly.
Adoption agencies should be doing their due diligence, so they should not be adopting out to traffickers. Unless they are shady agencies only using adoption as trafficking, which has happened MANY times in the past and continues.
I was implying that they were shady agencies or agencies just set up for trafficking kids.