Victoria it is perfectly natural to worry about your ds. Every parent is anxious about their dc being ok without them. This doesn't get any easier as they grow up. My ds (aged 12) has recently returned from a week skiing abroad and I worried the whole time he was away. The travelling, accidents, ski injuries, losing luggage, losing his cash, being ill, being unhappy, etc. But as parents we have to let them go. What's that saying? 'Parents give their children two things - roots and wings'.
I would strongly recommend allowing your ds to go on the trip but speak first to the teacher or TA about your concerns. I once had a terribly anxious parent confide her fears in me. Her child had never been anywhere without her and she was so worried. She asked me to please, please, please watch her child the whole time. So I made sure the girl was in my group, I made sure she was by my side all day, I made sure I was the one to take her to the toilet, etc. She had a lovely time.
Another parent told me that if her ds fell asleep on the coach he would be sick when he woke up, so I made sure I sat next to him and talked to him, played I-Spy and other games, so that he did not fall asleep. He had a lovely time.
And there is a huge celebration if we all get back to school without anyone throwing up on the coach because this so rarely happens
. But it doesn't spoil the day. The child recovers very quickly and has a lovely day.
Just pack a change of clothes (two if you think necessary) and let the staff know about travel sickness. Just try it, I am sure he will love it.