Once they learn what food is, they will not likely peck at anyone else unless they get stressed (too crowded, too hot, etc.), or they are establishing the pecking order. Right now you can sort-of think of them as little toddlers, "testing" everything by trying to put it in their mouths. They grow out of that. My worst offenders as chicks turned out to be great foragers as adults.
Instead of pecking each other, some chicks can be distracted by fun brooder "art."
Sometimes they are just bored, so giving them something to peck at can be helpful. You might put a small mirror in the brooder, or use a sharpie to draw stick figures or dots on a piece of cardboard that surrounds the edge of the brooder. This keeps them busy with something to peck at besides each other!
Some boredom-busting products like the Chick Jungle Gym can also help keep them occupied.
If a chick that is picking on the others will not stop and appears that they may cause injury, you will want to step in. In these extreme cases, you will need to separate the offender from the others with a section of chicken wire or mesh (making sure they can still see the other chicks and still have access to heat, feed, and water). Usually, separation will only be necessary for a day or two while the offender gets the hang of what is okay to peck at and what is not.