Child has one on hand for such gentle treatment (3,5)
I believe the answer is:
kid glove
'such gentle treatment' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Perhaps there's an association between them I don't understand?
'child has one on hand' is the wordplay.
'child has' becomes 'kid' (I can't explain this - if you can you should believe this answer much more).
'one on' says to put letters next to each other.
'hand' becomes 'glove'.
'kid'+'glove'='KID-GLOVE'
'for' is the link.
(Other definitions for kid glove that I've seen before include "Thin leather handwear" , "be diplomatic" , "Could be on hand" , "Overnice; delicate" , "What may be put on to handle delicate situation" .)