One growing up as prison child (10)
I believe the answer is:
stalagmite
'one growing up' is the definition.
(I've seen this before)
'prison child' is the wordplay.
'prison' becomes 'stalag' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'child' becomes 'mite' (I've seen this in other clues).
'stalag'+'mite'='STALAGMITE'
'as' is the link.
Can you help me to learn more?
(Other definitions for stalagmite that I've seen before include "Pillar of the underground" , "Column made by dripping water" , "What may form on cave floor" , "One that grows up" , "Upward-rising cave deposit" .)