Children are also responsible for themselves. Does the parent go to school and hand in homework to the teacher? If a child comes without it, can she say, "oh, my parent forgot to put it in my bag?" I'm very happy my daughter's teacher didn't let her get away with that one. She tried it once...the teacher said, "YOUR homework is YOUR responsibility." My daughter now makes sure she either packs her own backpack or the homework isn't sitting on the table. Otherwise she knows she'll be inside for recess as a consequence. This happened in the 2nd grade, BTW, when my daugther was 7: plenty old enough to take responsibility.
Miss a lunch or two and I'll bet children would start asking their parents for cash (school lunches are <$3) or remind them to put money on their accounts. Point is, I seriously doubt this was the first time these children had negative balances. We only heard one side of the story. I'd frankly be surprised if the school didn't have an auto-reminder set up re: lunch balances. Our school does. Note to parents: have your child carry around an extra $3 in a pocket of their backpack if you're the type that forgets to check balances or only puts a few dollars on at a time.