Lines for a child rising ten (6)
I believe the answer is:
sonnet
'lines' is the definition.
(poem of 14 lines)
'child rising ten' is the wordplay.
'child' becomes 'son' (male child).
'rising' says the letters should be written in reverse (in a down clue, letters go up).
'ten' backwards is 'net'.
'son'+'net'='SONNET'
'for a' acts as a link.
(Other definitions for sonnet that I've seen before include "14-line poem" , "Sent on the verse form" , "Verse form of 14 lines" , "Tonnes (anag.)" , "Form of poem" .)