Try putting some non-fat or skim milk in their drinking water, about 3/4 cup per gallon or 3 tablespoons per quart. This helps to promote a healthy digest tract by preventing a type of salmonella. Don't use whole milk. Also, try putting out a bigger pan of grit...I put out a bigger pan and was surprised by how much more my chicks ate when they could get to it more easily.
Hope this helps.
Hope this helps.