Every species, including worms and ants? Because they are surely smarter than 1-week old human baby, they can eat and move. We don't treat children well becaus

Every species, including worms and ants? Because they are surely smarter than 1-week old human baby, they can eat and move. We don't treat children well because of their intelligence - otherwise, no one would care about newborns. We care about them because they are of the same species as us. As for "dignity", I am not 100% sure what you mean, but in humans it comes directly with being able to function as a member of the society. For example, someone who cannot navigate city (be it because they are young or because of their developmental difficulties) will not be free to wander wherever they want.