Lively cartoon films are (8)
I believe the answer is:
animated
This could be a double definition.
'lively' is the first definition.
(synonyms)
'cartoon films are' is the second definition.
'animated' can be an answer for 'cartoon' (thesaurus). I'm unsure of the 'films are' bit.
Can you help me to learn more?
(Other definitions for animated that I've seen before include "Enlivened (like a cartoon film)" , "Lively in diamante" , "put in spirit" , "Full of excitement, lively" , "Diamante (anag)" .)