I prewash all fabrics on a gentle cycle in hot water and dry in a hot dryer. I want any and all problems known before I even start sewing.
Baby quilts will generally be washed in hot water by the buyer (even before using if they're smart), but I'd much prefer that I get any surprises first. Besides, commercial fabrics are treated with formaldehyde and other chemicals and that, to me, is reason enough to prewash, especially anything intended for babies.