Spend a couple 5-10 minute sessions with your birds each day. Give them treats, pick them up and hold them, talk to them, etc. After doing this for a few weeks, the chicks will be more used to you. You can begin to call them by name and let them come to you when called. It is just like training a dog, except they are a lot smaller and require a lot more attention! I hope this helps!
My babies are so different than my older chickens. They're so much friendlier and more confident than my older chicken who are more suspicious and wary. Maybe the babies will change but for now they sure are fun.
Everything the above posters say…but the breed has something to do with it. For instance, the previous group of chickens I had was a mixture of White Leghorns and Rhode Island Reds. The personality difference between the two breeds was huge! They even stayed in their own groups when free-ranging. And the Leghorns always reacted to me as if I were a stranger, while a couple of Reds would run to me to be picked up when they saw me outside.