There aren't any magpies in my backyard but I saw a crow once standing on a tree stump in the chicken's enclosure staring at them. I wonder what it wanted?
Red Stars ( also called Red Sex Links, Cinnamon Queens) are friendly too and they lay extra large dark brown eggs I had a Red Star that layed an egg almost every day even through winter.
It should be fine if you introduce your large fowl chicks at a young age to your bantams, mine get along with a few disciplinary pecks here and there http://www.the-chicken-chick.com/2013/04/when-to-move-chicks-from-brooder-to.html. My large fowl White Leghorns are very friendly and like to be...