A teacher going out with the students but a flood killed some of them

A: In case that reality is exactly as what you have mentioned in the question, you are not a sinner and no Kaffarah is obligatory on you (Part No. 21; Page No. 390) for the death of the three concerned students. This is because you did not neglect rescuing them. You did your best and rescued one of them, and you did not cause the death of the others, for when you took that way there was no flood, then the flood overtook you in the middle of the way as you mentioned.May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.