Stephanie, I understand your worries. Do your children want to go to camp or is this their idea? Maybe you should have a heart to heart with them, particularly your son, and ask him to imagine a day and night at camp in as much detail as he can. Talk to him about his worries and try to find solutions or helpful ideas together.
I was a camp counselor and there were a couple of kids who got homesick, but they were nurtured and loved through it. Those kids stayed for 3-9 weeks, even the 6 year olds, so they got over it eventually. No one had an over all bad experience. He's getting his feet wet. There are so many adventures in life and this is just the beginning. You want him to be free and confident and if you worry him he won't be. Fake it until you make it, if you have to.
My 7 yo daughter is about to go on a mission trip without me to a third world country. This is her first adventure without me and she's so young. We will be apart for 10 days, after which I will join her along with my 3 yo son. She was born in that country, but I'm nervous nervous nervous. My parents travelled the whole world for me and never made excuses based on fear, not even when I had malaria. It was the gratest gift they ever gave me. I have a kind of confidence in myself that I haven't seen in many people and it has served me well. I want that for my baby, so while I'm coaching her on being careful I will not let her see me worry. I don't want my feelings to weigh her down. I want her to fly.
Good luck.