Day nursery somewhat mediocre, cheap (6)
I believe the answer is:
creche
'day nursery' is the definition.
(nursery for children)
'somewhat mediocre cheap' is the wordplay.
'somewhat' indicates a hidden word.
'CRECHE' is hidden in the letters of 'mediocre cheap'.
(Other definitions for creche that I've seen before include "Tableau of the Nativity" , "Place where infants are cared for" , "Day nursery for infants" , "Nursery provided for working parents" , "Daytime nursery" .)