Could some families afford the cost and time of providing a better 2-4 course lunch every day? Sure, but most won’t.
This is why, for the first 4 years of school, I went to a specialized school for physically and mentally disabled children. I was not really disabled (besides allergies and asthma), but that was the only school where the cafeteria personnel was able/willing to accommodate my needs. (My grandmother brought in precooked food for me for the next day when she picked me up from school.) When I changed to secondary school, my parents employed some legal tricks to get me into a school close to my grandmother's apartment, so I could go to her place for lunch.
I realize that I was an edge case. But I sure hope that the laws governing those French kids accommodate their edge cases.
France gets a big fail on this one. It's incredibly difficult to completely dis-own your children in your will.