What are the reasons of the childrens' disappearance?

Presently there are many cases of  children's disappearance. The last in Córdoba when two brothers were  looking after by their father who has not given clear explanations about this stranger case.
Not only the police has found mistakes in his report, but also there were problems in his marriage.
Although, it seems an easy investigation for the police, after three weeks there is not a solution.

http://www.thereader.es/spain-news-stories/7208-Girl,-6,-and-her-two-year-old-brother-missing-in-Cordoba.html