More workers in departements
I would hire more adults. There would be more management at night and kids wouldn't be running it. Pay employees that deserve it more money.
Get to know your workers and give them the hours they deserve.
I would make the break room always have water and some free snacks for hungry employees. I would also brighten up the break room, as it was very plain. I would organize the bullet boards, bring in comfortable chairs with one big table so everyone can talk together. I also wouldn't hesitate to fire any employee with a constant negative attitude. I would also leave a box where employees can write down a conflict that they feel needs to come to me, then I would read the complaints and address them accordingly.
I would offer employees better hours. and a two week schedule.