How old are your chicks? Did they just start laying? When my chicks first started laying, they did that. I watched and realized it wasn't the hen who laid the egg, but others. They would come into the nest, step on the eggs that had been laid, one would break, so they had a snack. I then, like you, found out about making oyster shell available for them. So, I did that as well as I started going down to the coop several times a day and pick up any eggs. I now pretty much pick up all the eggs in the evening. The girls seem to like to lay in the same boxes, so occasionally one will be broken (and eaten), but not often enough to make me think it was anything other than an off-balanced hen stepping on a weak shelled egg. Be sure to take any debris out of the box. It's okay that they eat the shell, but it should be crumbled. I hope your situation is as easy a fix as this was. Good luck!