@Terry Again, your innocence and ignorance of child trafficking is adorable. Ever heard of falsified documents? Are you under some false impression that children can be brought in a country only by illegal immigrants? It's gonna be done via legal citizens of the country, that use all kinds of falsified documents to pretend the child belongs to them in some way (either as adopted or even passing as their biological offspring). These things are rarely easy to detect.
So "don't let them in" is just not as simple as you think.