Your chickens are in their "child" stage. They are not just sweet helpless babies anymore, they are learning to act like adults and explore the world in a different way. NEVER take it personally when an animal does something like that...pecking you too hard, cat scratching you, etc. The animal does NOT mean it personally. They are just being what they were designed to be, doing what they are meant to do. Your chickens are not being mean, they just don't know their own strength and how that peck actually hurt you. They are growing and changing, and all animas go through phases like this where they "act out".
I have(and currently do!) worked with SO many different kinds of animals over the years, and I have been bitten, pinched, scratched, cut, filleted(lol), b ruised...the list goes on...byh nearly all of my creatures. Sometimes it hurts EXTREMELY bad(cockatoo), sometimes not too much at all(small snake)...but I make a point of never letting it hurt my feelings. They don't mean it to do that, so keep that in mind when it happens and don't let yourself see it that way!