Christmas will be held up by little ones (4)
I believe the answer is:
noel
'christmas' is the definition.
(synonyms)
'held up by little ones' is the wordplay.
'up by' says the letters should be written backwards.
'held' indicates the answer is hidden within the clue.
'leon' is hidden within 'little ones'.
'leon' back-to-front is 'NOEL'.
'will be' acts as a link.
(Other definitions for noel that I've seen before include "Xmas refrain" , "- - Coward, playwright" , "Festivity" , "Festive season" , "Girl - boy - Christmas" .)