Urge children to be quiet inside (5)
I believe the answer is:
speed
'urge' is the definition.
(thesaurus)
'children to be quiet inside' is the wordplay.
'children' becomes 'seed' (I've seen this in other clues).
'to be quiet' becomes 'p' (music symbol for 'piano', ie soft or quiet).
'inside' indicates putting letters inside.
'seed' going around 'p' is 'SPEED'.
(Other definitions for speed that I've seen before include "Travel quickly" , "The going rate" , "Race" , "Rate of progress" , "Tempo - drug" .)