Kanga's son (3)
I believe the answer is:
roo
'kanga's son' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for roo that I've seen before include "Marsupial (dim.)" , "Young marsupial" , "Australian jumper" , "Kanga's child (Milne)" , "Jumping marsupial" .)