A lot of the malnutrition of students is driven by money. For instance Coca Cola has contracts with a massive chunk of all US school districts. And schools are obviously signing those with complete disregard for the health of their student in exchange for money. But because money is the motivation, this can just as easily be fixed by executive order (amongst a million other ways). Cut Federal funding to schools that sell soft drinks or other sorts of unhealthy products to children and Coke will disappear pretty much overnight.

Food deserts are largely irrelevant. Things like rice, beans, canned goods, and other such products are widely available and provide sufficient nutrition. There is also online food ordering (from Amazon etc) that allows payment with things like SNAP. And the sort of products we're talking about are not "treats", and should not be seen that way. They are highly addictive and harmful trash that, in the future will almost certainly be completely banned, certainly in anything like their current formulations.