You don't have to wash them first - as matter of fact, it's easy for them to become wonky when you do! And a pain to iron them :) Most people don't wash charms, jelly rolls, etc. But, if you do want to wash them, and I have before where the majority of fabric for a project was already washed, then I soak them in soapy water. Rinse gently, all done by hand, and lay out to dry. This method causes the least amount of damage to the edges.
I normally don't wash any of my fabric for any quilts. But, I will test reds and some of the dark blues. Never had a problem :)
Debbie in Austin