Children keeping dog locked up (7)
I believe the answer is:
secured
'locked up' is the definition.
(I've seen this before)
'children keeping dog' is the wordplay.
'children' becomes 'seed' (seed can mean one's offspring).
'keeping' means one lot of letters goes inside another (some letters kept inside).
'dog' becomes 'cur' (a cur is an aggressive or scruffy dog).
'seed' enclosing 'cur' is 'SECURED'.
(Other definitions for secured that I've seen before include "all tied up?" , "Made firm" , "Gained" , "Protected" , "locked up" .)