Stress
Sometimes stress can come from unexpected places. You might think the kids would stress you out the most: screaming and fighting over toys, refusing to eat or take a nap, or generally creating mayhem when you're scrambling to keep them in line.
Yes, they might drive you crazy. They may even make you wish you'd chosen a career as a lab researcher, where the only living things you encounter exist under a microscope and don't talk back. However, don't even think of taking out your frustrations on the children.
You might not anticipate the stress you experience from dealing with the parents themselves. They may flood you with barely-reasonable demands; or they might call you incessantly for updates on Little Susie's snack consumption, bathroom habits, or social interactions.
Your staff might also annoy you, but don't tick them off too much or you'll be running the entire place by yourself. Finally, the daily grind of operating the business may drive you to consume an entire pack of Little Debbie's once you get home.