Changing is never an easy thing. Neither get ou of the conforte zone. Specially if you have never seen and experienced different situations.
Putting a child who always heard the same things of his/her relatives ("you live in a favela and always will live", "this thing is not for us, it is just for the rich people", "our place is here") in a developed society will show him/her the way his relatives live is not the right way, they could build and live in a better environmental.
The sooner this chock is created, the sooner the future of this population will change. Because this inhabitants will not grow agreeing with their reality. They will battle to change their society, studying, promoting discussions and doing whatever they can.
The program is not only provide this trip abroad. After this, professionals will develop the children's ideas and wishes along their youth.