Kids Come Home SUPER Overstimulated

My kids come home SUPER overstimulated some days.  When I ask what they did at school those days they say.. "we were on our Chromebook all day." I don't even let them on screens after school because I know they have too much screen time at school.  Also, my oldest son’s first encounter with porn on a computer was during school... the district tech guy said that the school filtering system was "not very good at stuff like that." I don't understand how that is even okay to have that be the standard.