I fully agree with centrachid. I have in almost 60 years of chicken husbandry never seen an adult rooster even peck at a chick.
Now if you go into a pen or do something crazy or stupid and cause chicken drama or panic anything can and will happen, like a rooster or more likely the chicks' own mother killing one or more of her own chicks from collateral damage. She will do this by hitting you, hitting at you, or fighting with another hen, usually in a misguided attempt to protect her brood.
I have seen this happen more times than I can count and it was always my fault, but the crazy hen involved was never allowed to brood another clutch of eggs. Folks, you got to stop and remember that chickens aren't brain surgeons, they're totally controlled by their instincts and that no chicken can comprehend the results of its own actions. When the eggs hatch some hens undergo a complete personally reversal, be ready for it when she comes off the nest, and don't say that I didn't warn you.
I dont keep my chickens in a pen. They have a little room for them in which they sleep at night. But i totally agree with chickengeorgeto if you keepi your chickens in a pen!