Child with foreign currency brought back organ (6)
I believe the answer is:
kidney
'organ' is the definition.
(kidney is a kind of organ)
'child with foreign currency brought back' is the wordplay.
'child' becomes 'kid' (synonyms).
'with' says to put letters next to each other.
'foreign currency' becomes 'yen' (currency of Japan).
'brought back' says the letters should be written backwards.
'yen' backwards is 'ney'.
'kid'+'ney'='KIDNEY'
(Other definitions for kidney that I've seen before include "Character" , "Organ; kind; bean type" , "Internal organ producing urine" , "Organ filtering waste with water from blood" , "nature" .)