Stick whatever you have in there and see if they use it.. if so, then hooray! Also, I wouldn't worry about sterilizing a branch (just don't use one that has a bunch of say, bird poop on it). My chicks have a dowel and they use it all the time.
Thanks everyone! I have a few pieces of 2x2 that were left over from other projects that I might use. I know they don't really need it yet, but I have 6 that are about a week old and 4 that are 3 days old. They are starting to play leap frog over the each other so I thought I'd give them something to jump up on.