Mon Mon Mon Monsters is a Manga/Manhwa/Manhua in english language, Comedy series, english chapters have been translated and you can read them here. You are reading chapters on www.mgeko.cc fastest updating comic site. The Summary is

Shuwei, a quiet and deligent student was being bullied by his classmates. He was falsely accused of being the culprit who stole the class lunch money. As punishment, his teacher assigns him and the three main bullies to volunteer at an old age home. There, they encounter two human-eating monsters. They managed to capture one of the monsters and repeatedly conduct their own experiments on it in a secret basement. As event unfold, the true horror begins to reveal itself.