I was a bit nervous too, but D and most of his friends adjusted fairly easily to Kennedy. I think it helped they knew so many familiar faces in the playground and a couple in their class. Would recommend organizing playdates with other friends who are going to Kennedy, and if he does have a best friend you can request that they put them in the same class. D's Y1 teacher was amazing and the kids adored her, which made the transition so much easier. We still continued with our after-school activities. We only did two a week and the rest were playdates. But I did notice by Friday, he was pooped and would just prefer to crash on the sofa and watch cartoons.
I do feel that Kennedy is a big school and wish it was smaller and more intimate like Glenealy. But the facilities are better and the kids do enjoy using Stanley Ho's pool and grounds.
They don't tend to do joint activities with the other Y1 classes. You can also volunteer in your child's class and see how he's getting on.
HTH