I thought I'd add...because it sounds like you might need to CATCH a couple of cats and turn them over to the humane society.... Look for "dog proof coon traps"... They are a little paw sized tube, and you can put tuna fish in it, and the cat tries to dig the tuna out and gets its paw snapped shut on. Humane, easy, cats gone(a little tricky to get off of a mad cat, though)... I " accidentally caught my neighbors cat, so I KNOW they work on cats ha-ha
And I also add that I agree that they are just too young to be out with no fencing... They look delicious to a cat, so I personally wouldn't put them out AT ALL until they are bigger than "cat sized" bird...8-10 weeks, unless you build them a good solid run, and keep an eye on those cats...pellet gun and dog proof coon traps, those are our defense against cats