I couldn't find any sources for widespread beatings of children to death by teachers.
>Ahn noted that prisoners detained in the punishment chambers were often crippled after three months and dead within five months. Ahn and other former guards have testified to the brutality that they were encouraged to demonstrate while punishing prisoners. Former guards have confessed that they were taught not to view prisoners as humans. However, the number of deaths from beating prisoners was so high that at one point, the guards were encouraged to be less violent.
https://www.state.gov/wp-content/uploads/2019/03/Prisons-of-...
>One inmate recalls that as a 10-year-old he was told to lift a 30kg sack of earth (more than his own body weight) 30 times a day. If he slipped he was beaten with sticks by his teachers. Kang Cheol-hwan (former Yodok inmate. He was detained with family as a young boy). Here called: The work was too much for me or for any child of my age. But I did not dare to complain. After the first ten rounds, my legs started shaking, my body was hurting and my shoulder skin was peeling off. I was near collapse but the teachers were watching us and beating us with sticks if we stopped.”
>Kang Cheol-hwan also recalls deaths of children who were working at a work site. “The children in my class were ordered to dig and move earth to a work site 200 metres away. Twelve children dug holes with shovels and the other children carried the dirt in sacks or buckets. The dig site was a clay hill and the clay was quite soft. But we were afraid that as we dug deeper, it could collapse at any time. The teachers who were supervising us told the children to keep digging. After three days, the hill suddenly collapsed. There were six children who were on top of the hill when it collapsed. Three children were killed and the other three were badly injured. However, the teachers blamed the children for the carelessness.”
>Between the ages of 13 and 16, Shin recalled: “I was forced to undertake dangerous work and saw many children killed in work. Sometimes, four to five children were killed in a day. On one occasion, I saw eight people killed by an accident. Three men were working high up on a tall cement wall, three 15-year-old girls and two boys were helping them with mortar below. I was carrying mortar to the children when I saw the cement wall falling. Eight were buried under many tons of mortar; there was no rescue. Instead, the security officers told us not to stop work.”
https://www.amnesty.org/en/wp-content/uploads/2021/07/asa240...
>Security officials armed with machine guns gathered together all the political prisoners at the camp to witness the hanging of the two adults and the execution by firing squad of the three children.
>“Interviews were conducted with 35 defectors who had escaped from various detention facilities in the preceding 18-month period, and 31 of them testified to having witnessed the killing of newborns.”
https://web.archive.org/web/20141006072142/https://www.kinu....