I am looking for the short story that features a man describing a Mars settlement and how the new generation of Martians are so great and wonderful and whatnot. And at the end of the story, the Mars kids reveal their plan to kill every single remaining Earthling on their planet. Again, I read this story in one of the Megapacks.
A drug called Adaptine has allowed them to gradually change their anatomy and physiology to survive on Mars:
“In another ten years, at maturity, you will be completely acclimated to Mars. Its air will be your air; its food plants your food. Its extremes of temperature will be easy for you to endure and its median temperatures pleasant to you. Already, because of the five years we spent in space under gradually decreased gravitational pull, the gravity of Mars seems normal to you. “It will be your planet, to live on and to populate. You are the children of Earth but you are the first Martians.”
They have gone along with the plan, but don't want any 'aliens' on the Mars that they are so well adapted to.
Tomorrow, at a signal, we will kill the teachers and the other Earthmen among us before we go forth. They do not suspect, so it will be easy.