It also depends on the child's personality a lot. I know it would be a disaster for DS. Yes, he would love it. He wouldn't have to extend himself in social situations and could just coast along with a dozen other kids, making friends by default because there aren't many options in a small pool. But it would destroy him socially in the long run. It might be harder for him to join in a bigger group now, but it is a skill he needs to learn rather than hiding away and suddenly hitting high school with no means to make friends.

The kindy here only has about 25 kids on the roll atm, but at least they are all in the same age range and not spread over 6-7 year levels. Then the primary school has about 180 kids, so not too big but big enough.