as silkiechicken posted, sometimes it's a genetic thing.
no need for antibiotics unless they show signs of specific bacterial infection, such as respiratory.
some times it's the bedding they are on .
in the beginning they should be on a flat non-skid surface..such as the rubbery material used for kitchen cabinets that comes in rolls.
or deeply ridged paper towels.
many times it's a vitamin deficiency. (usually, but not exclusively, riboflavin..vit12)
could be a mal-absorption problem.
how many chicks are in the brooder?
what temp are you keeping them at?
please describe droppings..color and consistency.
what all are you feeding?
observe chicks eating and drinking habits.
if you are not giving chick vitamins, do get some asap.
or in the meantime, dlhunicorn suggests using Polyvisol children's vitamins..2 drops a day for a week, then taper off..
but do try to get some chick vitamins.
