It is a state rule. States have any number of weird rules to keep their control over minors. The goal is to keep them in public school as long as they can.
In my state I wanted to hire someone to clerk in my store a couple of days a week during the summer. There were several young people who were interested but the local school board, who does not like me, refused to give them work permits. I ended up having to hire from the next county.
I love it. if they pass the test there will be a lot more work for them beyond your 2 days. There’s 7 days a week. Let them. I’m 66 and I’ll give them a free ride if they don’t have a license or car. It’s like those Amish who wanted to vote Trump for the first time but had no autos to take them to the polls.