Device for gambling? Youngster needs short warning, is enthralled (9)
I believe the answer is:
totaliser
'device for gambling?' is the definition.
'youngster needs short warning is enthralled' is the wordplay.
'youngster' becomes 'tot' (tot is a kind of youngster**).
'needs' says to put letters next to each other.
'short' means to remove the last letter.
'warning' becomes 'alert' (alert is a kind of warning).
'enthralled' indicates putting letters inside.
'alert' with its last letter taken away is 'aler'.
'aler' placed around 'is' is 'aliser'.
'tot'+'aliser'='TOTALISER'
(Other definitions for totaliser that I've seen before include "Betting system" , "System of speculation" , "system for the better" , "Risky system" , "you can bet on it!" .)