Really bad element in baby's malady (7)
I believe the answer is:
abysmal
'really bad' is the definition.
(I've seen this in another clue)
'element in baby's malady' is the wordplay.
'element in' indicates the answer is hidden within the clue (I've seen 'elements in' mean this (I've seen this in other clues)).
'ABYSMAL' can be found hidden inside 'babys malady'.
(Other definitions for abysmal that I've seen before include "Appallingly bad" , "Very bad, poor" , "Extreme and deplorable as ignorance may be" , "Dreadful" , "Deep, immeasurable" .)