@monstergelo The kids were on a trip when their plane crashed on Bug Island. A lot of them were dumb and got killed/eaten by bugs. The group here escaped Bug Island on a boat but the place they went to seems to be Bug Island 2: The Revenge.
@S0lid_Sn4ke This is one of those manga where they kill off all the enjoyable characters so that they can preserve the drama. Even if the enjoyable characters were more attractive and that's really why anybody reads the manga in the first place.