I believe many of these parents just did not know that their kid’s account was low/negative on money. They just need to go back to the “pay at the window” policy. No more of these accounts, especially if parents/kids can’t keep track of the account. It was a little cruel to serve the kids and then take it from them...
In our school’s system we can set a balance level at which we get a notification email - I think I have it set for $10.
I imagine most systems have something similar.
On the other hand, if a student is just a few dollars in the hole they are still served.
If the deficit gets larger the school contacts the parents about the free/reduced lunch programs that are available.
Regardless of who pays, no child should go without lunch.