My chicks are 3 weeks old and I have been using wood shavings in their brooder for the last 2 weeks. I upgraded the brooder to a large box today and at first they didn't know what to think. Some even acted a little scared. They all know where their food is and are eating and drinking just fine. There are a few who have started scratching in the mulch/wood shavings and are eating them. Will this hurt them?