Do you know what breed(s) they all are?

Chickens do have a strict 'pecking order' as you have seen. The 6 week old is, in my opinion, about two weeks too young to be out in a flock without a mama for protection--I never introduce my chicks to the flock until they are 8 weeks old. But that can also depend on how aggressive or mellow your other chickens are.

I've got a chicken info site, the page on introducing new birds to the flock is here, it may help:

http://jackshenhouse.com/VSChickIntroducingNewBirdsToFlock.htm

But basically if the youngster is constantly hiding and being pecked, or actively being hunted for bullying, it's too much. The occasional peck is normal though. Just make sure there is ample food and water for all. I like to have at least two each of food & water containers so the bullies can't guard them all. Also make sure that the youngster has places to get away from bullies and hide if needed.

Also on this page, read the part at the bottom of the page, 'Introducing new chicks to the flock':
http://jackshenhouse.com/VSChickHensBroodiesChicks.htm

I'd also suggest reading the 'Chicken Psychology' page to get insight into the strange things chickens do. :)

You can help protect the chick by taking an active part and making it clear that you are it's protector--YOU are the new Head Rooster, after all and are now their lord & ruler! :) Chickens catch on to this pretty quickly and will recognize your 'I'm mama and this is my baby' stance.

Congrats on your flock and enjoy your chickens, watching chickens is better than TV!

Velvet ~:>