Child with foreign currency brought up organ (6)
I believe the answer is:
kidney
'organ' is the definition.
(kidney is a kind of organ)
'child with foreign currency brought up' is the wordplay.
'child' becomes 'kid' (synonyms).
'with' says to put letters next to each other.
'foreign currency' becomes 'yen' (currency of Japan).
'brought up' says the letters should be written backwards (in a down clue, letters go up).
'yen' in reverse letter order is 'ney'.
'kid'+'ney'='KIDNEY'
(Other definitions for kidney that I've seen before include "Excreting organ" , "Organ associated with steak" , "Bean-shaped organ" , "class" , "Bodily organ" .)