Emit cry of pain close to mummy, looking rather sickly (7)
I believe the answer is:
yellowy
'looking rather sickly' is the definition.
(yellowy can mean looking ill)
'emit cry of pain close to mummy' is the wordplay.
'emit' becomes 'yell' (yelling is a kind of emiting).
'cry of pain' becomes 'ow' (exclamation of pain).
'close to' says to take the final letters (the 'close' to the word).
The last letter of 'mummy' is 'y'.
'yell'+'ow'+'y'='YELLOWY'
(Other definitions for yellowy that I've seen before include "Somewhat aged perhaps" , "Looking a bit jaundiced" , "Slightly jaundiced" , "A bit like custard or mustard?" , "Rather like sixties submarine" .)