Little one is only half into 'Fantasia (6)
I believe the answer is:
infant
'little one' is the definition.
(I've seen this in another clue)
'only half into 'fantasia' is the wordplay.
I cannot quite see how this works, but
'into' could be 'in' and 'in' is found in the answer.
This may be the basis of the clue (or it may be nonsense).
'is' is the link.
Can you help me to learn more?
(Other definitions for infant that I've seen before include "Tiny baby" , "Rudimentary" , "Youngster" , "Very small child" , "Small boy" .)