A little one has fresh crêpes hidden (3-6)
I believe the answer is:
top-secret
'hidden' is the definition.
(thesaurus)
'a little one has fresh crepes' is the wordplay.
'a little one' becomes 'tot' (I've seen this in another clue).
'has' means one lot of letters goes inside another.
'fresh' is an anagram indicator (a fresh re-ordering of the letters).
'crepes' with letters rearranged gives 'psecre'.
'tot' placed around 'psecre' is 'TOP-SECRET'.
(Other definitions for top-secret that I've seen before include "Very hush-hush" , "Highest classified (information)" , "Highly confidential" , "Highly restricted (information)" , "(Of information) strictly not for public consumption" .)