Concede some had mittens! (5)
I believe the answer is:
admit
'concede' is the definition.
(I've seen this before)
'some had mittens' is the wordplay.
'some' indicates the answer is hidden within the clue (some parts of the word are used).
'ADMIT' is hidden in the letters of 'had mittens'.
(Other definitions for admit that I've seen before include "Stop being obstructive" , "permit to come in" , "Confess (to something)" , "Provide student with place" , "Fess up" .)