Vex a girl and some boys (5)
I believe the answer is:
annoy
'vex' is the definition.
(I know that vex can be written as annoy)
'a girl and some boys' is the wordplay.
'a girl' becomes 'ann' (woman's name).
'and' means one lot of letters go next to another.
'some' means to look at the middle letters.
The middle letters of 'boys' are 'oy'.
'ann'+'oy'='ANNOY'
(Other definitions for annoy that I've seen before include "eat" , "Nark - nettle" , "Irritate - pester" , "Irk" , "Bother, irritate" .)