Swim class and family birthday party

I bravely have Andy enrolled in a 18 month to 3 year old swim class, when I really should have him in the 6-18 month class. He is two years old now, but still at a 12 month old level, and non-mobile. However, I was brave, and put him in a class with his "peers". I was reading that it is important for Andy to do activities with normal children, but maybe they should be normal 12 month olds. Who knows. It is hard when the instructor says, "okay, now let your kids run around and explore in the shallow water", and there is Andy, just sitting there. Or someone will say to me, "wow, he is so calm, and not running away from you". Lately, I just don't want to explain anything, so I don't. I almost feel like I am going to make them feel bad for saying what they said. But they aren't thinking when they say things to me, so why should I be so protective of their feelings? It is so confusing lately, on how much to say to someone, or just let it all slide.

The family birthday party went well, in the way of good weather, and good behavior from the kids. Andy has had a bad week, so it was nice to see him enjoying himself. I had a few comments from family members like, "Andy is doing so well", and "he's fine, don't worry", but easier said than done. I don't know why they say it. Maybe they feel I need reassurance. I'm sure they can see my anxiety over it. I just don't say anything back to them either, because I just don't know what to say or think anymore.