Support item during early development stage … (8)
I believe the answer is:
teething
'during early development stage' is the definition.
(as in a baby teething)
'support item' is the wordplay.
'support' becomes 'tee' (tee is a kind of support).
'item' becomes 'thing' (I've seen this in another clue).
'tee'+'thing'='TEETHING'
(Other definitions for teething that I've seen before include "It'd painful for baby" , "Occasion of initial troubles" , "Painful time for baby" , "The process is painful for babies" , "problem in infancy" .)