Can you set up a feeder that's too high for the chicks to get into, but at a good height for the hen. It should be level or just a teeny bit higher than her back.
Also, iffin it were me I wouldn't be giving the chicks that much treats. Once a day is fine, but they really need the complete nutrition of their starter right now. But that's just me.
Well the chicks can jump up pretty well, so I think they would probably be able to get to it, but we will try that and see how it goes.
The chicks still eat a ton of their food. But we make oatmeal from chopped whole grain oats, quinoa, raisins, cranberries...so we don't consider it a treat because everything in it is very fresh and nutritious.