Little sibling that's revolting teenager initially took along (7)
I believe the answer is:
brought
'took along' is the definition.
(I've seen this in another clue)
'little sibling that's revolting teenager initially' is the wordplay.
'little sibling' becomes 'bro' (short for 'brother').
'that's revolting' becomes 'ugh' (I've seen this in other clues).
'initially' indicates taking the first letters.
The initial letter of 'teenager' is 't'.
'bro'+'ugh'+'t'='BROUGHT'
(Other definitions for brought that I've seen before include "Took along with you" , "Caused" , "Contributed" , "Carried (to a place)" , "Delivered or carried" .)