Time of celebration may be held up by little ones (4)
I believe the answer is:
noel
'time of celebration' is the definition.
(Noel means Christmas)
'held up by little ones' is the wordplay.
'up by' shows that the letters should be reversed in order.
'held' indicates a hidden word.
'leon' can be found hidden inside 'little ones'.
'leon' backwards is 'NOEL'.
'may be' acts as a link.
(Other definitions for noel that I've seen before include "Xmas refrain" , "Christmas; man's name" , "Christmas, in cards" , "Christmas, esp. in carols; boy's name" , "- - Coward, playwright" .)