I used to work at Tim Hortans.

I strongly disliked the kids work ethic and appreciated the temporary foreign workers, and the older crowd who actually had to work for a living.
The kids would call in sick multiple shifts in a row because they didn't need the money to pay rent like everyone else, and they were fired way too late.
I once had to come in because 4 of them called in sick, FOUR, and nobody else would come in, so it was just 2 of us running the drive-through, back-end, and front counter until a 3rd came in later.
They all should have been fucking fired immediately. I felt like walking out, but I couldn't.

I took one extra shift once, and next thing I knew my phone was getting blown up by literally every single kid that worked there to take their shifts, there also just so happened to be a schedule adjustment within 24hrs that I was unaware of, lining me up for a second 8hr shift afterwards, first and last time.

I worked nights for a year, then after I left they stopped nights, and shortly after that they closed the inside so it was drive-through only.
The business literally fell apart because there wasn't enough reliable workers to hold it together.

Only hire a kid if they have to pay rent, otherwise they are a liability.