I would say that we must wait for more news.
In most EU countries as France or Spain, when a child is separated from his parents and his identity is unknown, the child is given an assumed name pending further findings by the Registrar Officer while he is entrusted by a guardian or Social Services, under Juvenile Court's oversight.
Even if the child's circumstances are all over the news, there are other missing children from the attacks.
So, if the child is living, he is probably under an assumed named and treated as a John Doe pending further checks about his identity. It can take a few days for checking accurately his identity : it's not enough that he is recognized from a photo in the news, we must have accurate material evidence of alleged identity.
With so many victims in the attacks, it takes time for LE to check all victims identities even when they are informed by Social Services about unidentified children in care because of the attack.
In France, it really took two weeks after the Bataclan attacks to identify all unidentified hospitalized victims. I doubt that LE can go quicker than the music !!
If he is dead, even if he is positively identified by the family, DNA testing can also take a few days.
Family might recognize the body while the DNA check says that the body is not of family member, and vice-versa.
And the photo of said child is too blurry for accurate identification. Especially because it's obvious that said child is from behind on the photo. Think also that the child didn't carry official identification on his person.
So, we won't know before more official news.
His missing poster is still available on SOS Desaparecidos twitter feed. Means that said child has not been located yet with certainty. Otherwise, the family and/or LE/foreign government would had released a statement.
When a missing person is located with all certainty, SOS Desaparecidos recovers the photo with a sign stating "Located safe" or "Located deceased, RIP".
Unless and until more news, we shall refrain from rumors and speculations. Such attacks are a real chaos, so getting accurate info about missing persons in such circumstances is more difficult because material elements are very difficult to find.