"Critically Ill" Children disappear from hospital in Austria

So....

Illegal immigrants are found in a van in Austria.  The children are critically ill and are rightly treated in hospital.

As they get better they mysteriously vanish from the hospital and disappear into the ether.

How can the Austrian authorities be so naive as to think that people who are not prepared to play by the rules in getting into the country will play by the rules once they are in the country?