Signs and behaviors. That requires some thought. It is pretty normal for older chickens to be curious when they first see young chicks. They can gather around and may peck some, chickens often explore with their beaks. That doesn't worry me.
If immature chicks invade the personal space of older chickens, they are liable to get pecked. It doesn't happen al the time but it happens often enough that younger chickens usually learn to avoid the older ones, to try to not invade their personal space. When they first get pecked they run away. The other chicken may or may not chase them a bit but usually they get way without a problem.
The problems come in when they get trapped and cannot run away. If that happens the older chicken may stand over them and peck them, often going for the head. That is dangerous, they can kill them. That's why having enough room is important.
You can get a hen or pullet that does not let them get away. They chase them down and start pecking them, usually at the head. Or they will even go after them even if they did not at first invade their personal space. I've never seen this myself but people on here I trust say they have. My experience is more when they don't have room to run away they are in trouble. Even that is rare, but I have a lot of room.