We have 6 chicks 4 we hatched two bought from feed store - this morning two were dead. Guts missing, eyes gone. They are in a secure pin. Did they do this to each other. 1 was the one we hatched the other was from the feed store.
Definitely a predator, I am so sorry. Everything eats chicken, you need to seal up all holes and spaces bigger than a 1/4 inch. Do not use chicken wire on any external parts of pens, runs and coops. Things dig, so bury wire, railroad ties, etc ...and deeply. And use a solid roof.
Sorry for the losses. I agree with the other greeters, they were killed by a predator so if we could see a picture of your set up, maybe we could help you reinforce it to prevent further losses.