Knights taking great care to protect youngster (8)
I believe the answer is:
paladins
'knights' is the definition.
(I have seen 'Heroic knights ' mean 'paladins' so perhaps 'knights' could also mean 'paladins')
'great care to protect youngster' is the wordplay.
'great care' becomes 'pains' (I've seen this in another clue).
'to protect' means one lot of letters goes inside another (inserted letters are held or protected).
'youngster' becomes 'lad' (a young boy).
'pains' placed around 'lad' is 'PALADINS'.
'taking' acts as a link.
(Another definition for paladins that I've seen is " Heroic knights".)