Little wonder! (6,7)
I believe the answer is:
'little wonder' is the definition.
The definition suggests a singular noun which matches the answer.
'little wonder' is the wordplay.
'little' becomes 'infant' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'wonder' becomes 'prodigy'.
Can you help me to learn more?
(Other definitions for infant prodigy that I've seen before include "junior mastermind" , "Mozart?" , "Wonder child" , "Young genius" .)