Having had some serious experience with both pit bulls and dog attacks as well as fostering and teaching problem dogs I feel I may have something to add. First, are your dogs males? Are they neutered? If they are males and NOT neutered than let me suggest doing that asap. The term "has a pair" refers to not only the physical characteristics but also the attitude. If you're not breeding, snip 'em. Especially if you're letting them run while you're not at home or supervising them. The world does not need any more pit bulls (or any dogs for that matter) who need homes. There are enough dogs who are put down every day. Be responsible for your dog. You wouldn't let your child run out the door looking for a "good time" without discussing the ramifications of their decision. Dogs can't talk and it is a male's nature to dominate - and making puppies is a way of dominating another.
Which brings me to my next point, supervision. It always amazes me how individuals will not let their kids roam free without some sort of supervision, either theirs directly or another child's parent(s), but have no problem opening the back door and letting their dog(s) run free. Dogs are not people. They need to be taught right and wrong. If you are not supervising your dog(s) then you should not be surprised when they do something they are not supposed to do. And that goes not only for killing another pet or animal but also for peeing or pooping in the house or grabbing something off the counter. Granted you cannot be there all the time but if one takes the time to teach, the majority of the problems can be avoided.
Finally there is truth to the pack mentality. Dogs are not loners. They are social animals, much like people, and prefer to run in packs. You may or may not be aware but a family with one dog is actually the dog's pack in their eyes. They view themselves as the protector, as the alpha in the number one position unless they are taught differently. How does one do this? By controling the food, not by putting a bowl of food down on the ground in the morning and letting them have their food whenever they want it. By teaching them to sit and stay before releasing them to eat their food, not by pushing them out of the way as you put their food in the bowl and then down on the ground. By teaching them to walk beside you and not out in front of you, pulling you down the street. There are a number of exercises and lessons but these are just a few. The point is this: if you do not take the time to teach your dog what is right and wrong then they will take the initiative to do what they want to do. And if there is a pack involved the pack will rule and overcome any single thought and action. I always try to tell clients to think of this as a "mob mentality". Once a mob starts people in the mob make a decision - to either participate or not. Once a mob starts it's like a snowball effect. You just cannot stop it as it continues to roll and gain momentum. One person in the mob may decide not to include themselves in the mob's actions but they cannot stop the mob by themself either. It's the same with dogs. If the pack does it, then it's ok. And as the pack does whatever it is doing the feeling of accomplishment or approval begins to escalate and the energy level increases until the activity is over or another subject is located to turn their attention towards.
Now getting back to your issue. If you do not feel safe or comfortable having these dogs around your children or pets, then locate a pit bull rescue group and hand them over. Be sure you tell them they got into your chickens. The insecure feeling you have is felt by your dogs, believe me. And that insecurity will result in a bite or worse. Experience has shown me that pit bulls, more than any other breed I have worked with, pick up on insecurities. And couple that with the inherent characteristic of the pit bull breed to dominate and you have a recipe for disaster. If you have problems locating a local pit bull rescue then speak with your vet, they generally have more resources than we do. If you are still coming up empty, PM me and I'll be more than happy to assist. However, if you are not insecure and want to keep them then get into an obedience school (after you have neutered them) and re-enforce it daily. Pit Bulls are great dogs but just like any other thing that is dependant upon us need to be taught right and wrong, what is acceptable behavior and what is not.