On this topic, I find it disappointing (at least in the footer and the "English explanation of WikiKids") that Kennisnet hasn't made the project's content available under a free license. On edit pages it notes:
"GEBRUIK GEEN MATERIAAL DAT BESCHERMD WORDT DOOR AUTEURSRECHT, TENZIJ JE DAARTOE TOESTEMMING HEBT!"
which means:
"USE NO MATERIAL WHICH IS PROTECTED COPYRIGHT, UNLESS YOU HAVE TO THIS END AUTHORISATION!"
But beyond shooing away plagiarism, there doesn't seem to be any obvious mention. They've even removed the default mention of the GNU FDL that appears by default on Wikia hosted wikis.
Nick