Can you tell us their age and where you got them? Sneezing can have an environmental cause, such as dust in the feed or the bedding, mold, and water spills in the brooder which will quickly mold. Look for any air under the skin on the chick that is clicking. My chick once had a leaking air sac from a hard bump, and it cause a balloon-like leak under the skin. A respiratory disease might also be the cause, and that is usually from exposure to older chickens who are carriers of a disease. Can you see any bubbles or foam in the eyes of the sick chicks?