Mischief-maker chasing child's a little monkey (5)
I believe the answer is:
chimp
'monkey' is the definition.
(thesaurus)
'mischief-maker chasing child's a little' is the wordplay.
'mischief maker' becomes 'imp' (I've seen this in other clues).
'chasing' says to put letters next to each other.
'child's' becomes 'chs' (abbreviation for child).
'a little' means to remove the last letter (the word is not quite complete).
'chs' with its final letter taken off is 'ch'.
'imp' put after 'ch' is 'CHIMP'.
(Other definitions for chimp that I've seen before include "Creature" , "Anthropoid ape" , "Cheeky primate" , "Ape (colloq.)" , "A great ape (abbr.)" .)