I think it should not. Chocolate milk is nothing but skim milk, very processed and loaded with sugar. It’s not good for kids... most are already overweight, obese and have adult health issues. Why offer more sugary, processed foods/drinks ready available for them? Offer full-fat no added sugar milk instead in schools.
The food offered in school lunches has always been a political matter and it always will be. It has always been whatever was available and cheap and it always will be. The only way to protect your kid is to get your kid out of public school and ... probably into a school outside the country.