I am sorry for your lose, but don't beat yourself up. I got my chicks for the first time in April after researching everything about chickens for a looonnnggg time. So I am not an expert by any means. First I am suprised that you were able to just order 4 chicks. I ordered mine from McMurray Hatchery and only lost two out of 31 chicks. Which they and like many other hatcheries require a 25 chick minimum so the chicks stay warm during shipping. I think that it could have been a shipping problem for sure. I would try getting your replacements for either a local feed store or a farm swap so they won't get stressed from shipping. Good Luck!