Sketch several kids in trousers, first of all (4)
I believe the answer is:
skit
'sketch' is the definition.
(short comedy performance)
'several kids in trousers first of all' is the wordplay.
'first of all' suggests taking the first letters.
The first letters of 'several kids in trousers' is 'SKIT'.
(Other definitions for skit that I've seen before include "Short comic piece" , "Short satirical performance" , "Lampoon" , "Burlesque - parody" , "Parodic sketch" .)