Needing a win to qualify as Group G runners-up and join Fulham in the knockout stages of the competition, coach Ben Petty rang the changes following Monday's narrow Premier League 2 defeat to Southampton, making five in total, including a return for Will Alves in midfield after injury.
Wanya Marçal and Tawanda Maswanhise, both of whom have had First Team minutes this term, also came in. Leicester were on the front foot from the off at LCFC Training Ground and it was Portugal youth international Marçal who found the breakthrough on 18 minutes.
Silko Thomas, recently named in a senior matchday squad for the first time, doubled the Foxes' advantage just before the break, turning home the second four minutes into first-half injury-time.
A Iwan Morgan penalty shortly after the interval halved the deficit for the visiting Bees, but substitute Oliver Ewing re-established City's two-goal cushion with a quarter of an hour to play.
Kyrell Lisbie turned in what proved to be a consolation for the away side late on, but it's Leicester who march on into the next round, finishing the group stage on nine points from six games.
It was a remarkable turnaround from the Foxes' youngsters, who were without a point three matches in, but managed to win all three of the reverse fixtures against Brentford, Fulham and Burnley to make it through.
The details...
City: Doherty; Cover, Grist, Godsmark-Ford, Wormleighton (c); Cartwright, Alves (Ewing 62'), Briggs (Briggs 85'); Marçal, Thomas, Maswanhise (Pennant 81').
Unused subs: Young, Amartey, Richards.
Goals: Marçal 18', Thomas 45+4', Ewing 75'.