Don't belabor the point. When you feel homesick, you may feel kind of sad in your stomach. It just means you miss us. But the feeling goes away after a day or so. It's just a feeling, and it won't hurt you.
Most kids do feel a little lonesome.
When you feel that way, the best thing to do is some fun activity. Then later that night you can call me and tell me all about your day. If your child protests your leaving, try to find out if he has any legitimate concerns. Maybe he needs to be introduced to another child or the camp counselor to feel more at ease. If your child calls you later on, be optimistic and upbeat.