Children’s sugar consumption has been marked out as an important area of public health policymaking in the UK, due to connections between sugar consumption, obesity, type 2 diabetes and dental decay. Yet unlike other regulated substances (alcohol, tobacco, e-cigarettes), ‘moderate’ or ‘responsible’ sugar consumption, rather than abstinence, is the desired policy outcome. Based on ethnographic fieldwork in Edinburgh in 2018–19 in two demographically mixed Scottish state primary schools, I examine how school staff navigate this space of lenience written into state health policy—whereby some sugar can be consumed, sometimes. The public health dangers of sugar consumption, coupled with its relational pleasures (through associations with kinship, nurture and celebration) help illuminate how schools—as responsible agents—attempt to care for and govern children. It is sugar’s ambiguity, I argue, that enables it to become a crucial tool for children’s socialisation. Where and how sugar can be consumed responsibly, and which pleasures are deemed permissible or excessive, vary contextually: they are shaped through social class, and depend on the school policy being enacted. Beyond being an object to regulate, children’s pleasures in sugar are central to affective, social and class-informed practices of creating morally responsible persons.