Thanks everyone. This is all still quite new to us, so hearing what others (would) do is great. I'm still learning about what situations he does/doesn't cope well in, and I've never had to take him anywhere like this before, so didn't know it'd be an issue. He is no problem at my chiro/ob/physio appointments, and I figured with plenty of toys to play with it'd just be an extension of that. I did make a general comment as we went in both times, apologising that he was with me and saying that he was likely to talk through the whole thing, but I didn't say that it was due to sensory issues. Most people have never heard of SPD anyway...

Interestingly, his 3yo kindy teacher doesn't think I should say anything to his 'big kindy' teacher next year. Surely if there's anyone who needs to know, it's his teachers? I should arrange an interview for the beginning of school next year, shouldn't I?