Little child wanting a black horse (3)
I believe the answer is:
bay
'horse' is the definition.
(bay is a kind of horse)
'little child wanting a black' is the wordplay.
I cannot quite see how this works, but
'a' is within the answer.
'black' could be 'b' (as in pencil classifications) and 'b' is located in the answer.
A single letter 'y' remains which might be clued in a way I don't see.
This may be the basis of clue (or it may be nonsense).
(Other definitions for bay that I've seen before include "Botany, Galway or Tampa" , "Indentation of a shoreline" , "Reddish-brown horse" , "Part of sea" , "Laurel tree - bark" .)