If they are not full grown, I think it's likely a cat would go for them. Maybe you could let them out only when you can be right there, to watch for the cat? If it shows up, you could scare it off with a squirt from the hose, or something... I have both cats and chickens; when my cats showed interest in the hens, I threw a 'noisy can'. These are Altoids mint tins with several pennies inside, taped shut. They make a pretty good racket, and they are heavy enough to throw a good ways without being heavy enough to do any damage. (I should note that I had the chickens before the cats.)