If the food you are giving them is layer pellets you don't want to keep feeding that to them, to much calcium. If it's a flock raiser type feed then that's fine, otherwise need to pick up a bag of chick starter for them.
Chicks are healthy when you see them running around, peeping softly, eating and drinking when they are awake. They will nap frequently. Chicks that stand hunched up or puffed up with eyes closed, off by themselves, not wanting to eat or drink.....that is a sick chick.
Keep an eye out for coccidiosis, probably the most common problem chicks are faced with. Good idea to keep Corid on hand just in case.