I went through something similar last year with DD. She has a fear of small animals (cat/dog size and smaller). And of the furry/feathery variety.. They had an excursion to a farm, she didn't want to go. Her fear seems to be magnatised by about 10 whenever she knows I am around.

In the end, we had talked about it and she went. I made sure the teachers were well aware of her fear, and they inturn told the parent helpers there on that day. She was ok, but did have a few panic attacks handled well by the people there. As part of the excursion, the class had to do a talk about the day, so she would have felt more left out had she not gone.

I agree with not sending to school for the duration of excursion. At prep age, they are too young to run errands, so can't be made to feel useful if they are missing out and they probably be quite bored and not in their normal environment.

From the suggestions you mentioned, I would be inclined to offer to go if your presence will have the calming effect (as mentioned, my presence wouldn't have helped, only made it worse).

Being a movie, it does change my perspective a little. Is the day just about a fun day out? Yes, don't force it. Or is there an educational side to it? If this is the main answer, I would be working out ways for him to go, but if nothing seemed feasible, asking teacher for alternative. (I know nothing about the movie, off to google now)..