Do these kids not get outside in the 18 hours per day they are not in school? Surely they don’t get only 20 minutes out of the entire day to relax, right?

No one WANTS to take recess away from kids. But seeing as how parenting isn't being done at home, and schools have very limited ways to punish kids otherwise, it seems like a very reasonable way to handle this situation. As is almost always the case, be a goddamn fucken adult, and parent your crotch fruit.