Hi JonA, my DS7 has also been skipped two years and is due to go on a five day field trip with the older kids in July. DH and I have decided to say no for a number of reasons:
1. Our DS doesn't want to go (this bears the most weight for us)
2. He has already encountered a little bit of teasing etc. from the older kids (mostly from a new boy and also a girl who is very jealous) - this culminated in an incident where he was "pulled about" by the older kids for a laugh until another one put a stop to it. DH and I just feel that with such a large age gap he will be vulnerable (he will be just 8 and the others will be 10, some almost 11)
3. It is a very "active" trip and being quite a bit younger he wont be able to keep up with swimming, climbing etc.

This is just what works for our family and your situation is obviously very different (for a start your DS wants to go). That you are also able to accompany him for some of the time also makes a big difference. Have you tried to discuss your concerns with him? Good luck with your decision. smile