My girls used to do a lot of pecking at my pants and feet when they were younger, although I have one girl, 24 weeks old that still pecks on my pants. Chickens have only their beaks to taste, feel textures and to touch. So they are going to put their beaks on everything. I don't think you can stop the pecking. Now if they are open beak biting, then you might want to use your index finger to the top of their heads like they do to each other to show them you are boss. But it sounds like they are just enjoying your company.