Opening the bowling, 17-year-old fast bowler Campbell claimed a vital 2-14 from her four overs to help restrict Northern District to 3/119 from its 20 overs. In reply, Player of the Final Bess Heath (65 not out from 36) guided the students to 6/120 after Universities were at one stage 6/63.
Wicketkeeper-batter Darke, 18, and Campbell made their Sixers debuts in the opening match of WBBL|05, also at North Sydney Oval, a little under a month ago against the Sydney Thunder.
Another Sixers teenager Alisha Bates performed well for the runners-up. The left-arm spinner claimed 2-15 from four overs and made 39 from 45 balls opening the batting.
She was stumped by her Sixers team mate Darke after sharing a 72-run partnership with Northern District top-scorer Anika Learoyd (55 not out from 53).
Bates, 17, signed her first professional contract with the Sixers in October.