It is possible to accommodate in Italy adopted children for the holidays?

No.
In the first place, this could harm a child because it entails a dramatic uprooting from their own culture into a completely different world.  It would nurture hopes that cannot be fulfilled, other than the desperate dream of a clandestine immigrant to return to that “magical” world of riches and well-being, once he or she has grown up.
It is eminently feasible, on the other hand, for the sponsors to stay at the mission in Adwa any time, after making arrangements with the Association,  and to see the child in its own environment.