Five-year-old Artur's backpack was found at the mouth of the torrent. The backpack found earlier last week, it has been clarified, was his sister's.
The search off S'Illot has had to be suspended.
At least ten people including two Britons were killed. Six people still believed missing (updated at 18.00, Wednesday).
The prosecution has reached an agreement over the actions taken by air-traffic controllers in December 2010.