This is not really abt them protecting children, but well I have two on my mind, both is manga and leaning towards revenge !
https://www.mangago.zone/read-manga/ijimeru_aitsu_ga_waruinoka_ijimerareta_boku_ga_waruinoka/
a teacher's revenge to a student's father which is his old classmate (bully)
https://www.mangago.zone/read-manga/maria_no_danzai/
a revenge for his son who is bullied by some 'kids' (this contents violence, gore ?, well a badass teacher (mom) u got here).. first chapter is sad
https://www.mangago.zone/read-manga/koko_wa_ima_kara_rinri_desu/
Then how abt this ?
https://www.mangago.zone/read-manga/youkai_gakkou_no_sensei_hajimemashita/
And this one is abt a teacher at yokai school I think
https://www.mangago.zone/read-manga/yoarashi_ni_warau/
Also this ? It's abt bullying too
Idk if it counts as protecting but this teacher ATE THAT SHIT UP. I love the psychology lessons it brings and I LOVE HIM AS A PERSON!!!!
https://www.mangago.zone/read-manga/koko_wa_ima_kara_rinri_desu/
Here you go darling, enjoy!
https://www.mangago.zone/home/mangalist/2265824/
Recommendations for any teachers centric or stories where teachers took a sort of badass protective roles for their students, I'm imagining something like Royal Tutor, MHA, Great Teacher Onizuka, KHR, Iruma-kun (n the mafia spinoff), Yokai Gakkou, and more recently Sensei! Bokutachi ga Sekai wo Horoboshimasu!