I pre-wash my flannel fabric because I have read on here how it shrinks. And I have not pre-washed flannel and haven't had a big problem. But I have recently experienced a real good reason to pre-wash!!
My daughter called me last evening - her baby is now 2 weeks old - and Mom needs some more of those burp cloths I made for her shower gift! So I grabbed some flannel out of my stash and whipped up two more cloths and delivered them to her today, just in time to burp the baby and have the cloth catch the spit-up!!