Cardi, there is anxiety where you are irrationally worried about something, and there is rational anxiety which would cover the possibility that a very small child won't enjoy a very long trip.
I don't think this situation is clear cut. It very much depends on the child and his character and his feelings about long journeys and so on.
Why would they be scared, with all their friends and the teachers they know well and trust?
Can you remember being four, five? I can, and a lot of things that were new to me, freaked me the hell out.
I certainly didn't feel I knew or trusted my teachers or friends at school. Everyone seemed extremely tall, rather frightening, and sometimes a bit mad. I felt very powerless.
I wouldn't want to put one of my children in this position if I felt that they may feel the way I did. At that age I would have hated to go on a long trip away from home. I didn't even want to be at school - quite a lot of children cry every morning in reception.
I think the OP needs to decide based on her knowledge of her own child and the likelihood that he will enjoy it, or not. Not on the arbitrary call of a load of strangers who have never met him.