Do you provide grit in a separate dish or container so the chicks can take as much as they want or need, any time they want?
How old are the chicks?
Is their feed available to them all day, or do you feed at certain times? If at certain times, when and how much do you feed, and how many chicks are we talking about?
What breed(s) are the chicks/ chickens, and are all of them losing weight or just some of them? If just some, which ones? Are those losing weight housed together, or scattered in different coops? Have any died or look like they might? Can you get a stool sample to a vet and ask for a float test to check for parasites? Any vet can do this, it doesn't have to be an avian vet. It won't cost much, but if any of these birds have worms you can then know what to treat for.
Can you check their crops in the morning before they've had access to food or water to see if they are empty? If not, report what the crop feels like. Hard, soft, firm, squishy, full, gritty, etc., and if there is any odor. This info will help the experts to help you.