Gas caused distress for baby (7)
I believe the answer is:
neonate
'for baby' is the definition.
(medical term for a newborn child)
'gas caused distress' is the wordplay.
'gas' becomes 'neon' (neon is a gas).
'caused distress' becomes 'ate' (I can't justify this - if you can you should believe this answer much more).
'neon'+'ate'='NEONATE'
Can you help me to learn more?
(Other definitions for neonate that I've seen before include "Recently born child" , "One in delivery ward" , "New baby" , "Young baby" , "very young child" .)