I do not free range my bantam chickens nor my heritage breeds, the first ones because they are small and the second because they cannot clear the 4ft fence to get out or back in.
I do free range my poultry with precautions. At first I worried about the bantams because they are so very small and I kept them locked up, but then after I let them free range under the watchful eye of a human or one of the dogs I realized they were the best fliers of any birds I had. They can take to the air in a minute and almost nothing is off limits to them, even finding them on the roof of the house. So when the big birds are out, so are the little ones.
Also, during the day, they are excellent about staying under things. Usually they forage under ever greens and bushes and if you didn't know where to look, you won't see them.