Infant prodigy is hardly to be marvelled at (6,6)
I believe the answer is:
little wonder
'hardly to be marvelled at' is the definition.
I know nothing about this answer so I can't tell whether this works.
'infant prodigy' is the wordplay.
'infant' becomes 'little' (I can't justify this - if you can you should give a lot more credence to this answer).
'prodigy' becomes 'wonder' (I've seen this in another clue).
'little'+'wonder'='LITTLE WONDER'
'is' is the link.
Can you help me to learn more?
(Another definition for little wonder that I've seen is " It's not surprising".)