Chicks do not need grit. They should be eating a quality chick feed developed and formulated esclusively for chicks. At this young age all that they need will be in their feed. Treats should not be fed to them for the first few months. Treats dilute the chick feed that they need to be eating to grow properly. Chicks do not have many taste buds I think that they might have 10 or so. So treats at this age do very little good.
Once they are older and are outside if you free range they will find things here and there in the ground. If you use sand as a bedding in your pen they will use that for grit. If you are still worried at that point you can get some grit and put in a dish in their pen for them to have access too. But for the first 3 months or so of life they need to be fed only their chick starter feed. That has all that they need including the right ration of grit to digest their feed. They less you supplement at this young age generally the better.
Once they are older and are outside if you free range they will find things here and there in the ground. If you use sand as a bedding in your pen they will use that for grit. If you are still worried at that point you can get some grit and put in a dish in their pen for them to have access too. But for the first 3 months or so of life they need to be fed only their chick starter feed. That has all that they need including the right ration of grit to digest their feed. They less you supplement at this young age generally the better.