Out of curiosity, did your kids entering K have peers who were also reading /advanced? Did they tend to pair up together as friends? My DS would love having a friend who loves science /geography /math as much as he does. He goes along with superhero-ninja-spies play because his friends love it.
My kiddo didn't have peers at his educational level when he entered K, but it worked out OK. There was so much new to him just in learning how to "do school". And he had other friends in his class that weren't at his level, but with shared interests (like Lego). DS didn't make close friends until he was in a program specifically for HG kids, in 2nd grade. Could also be the normal time developmentally for him to make friends.
DS made friends out of grade level too in afterschool activities like Lego league. We got special permission for DS to take some of those classes even though not normally open for kindergartners. (Once you get on a roll with advocacy, you learn that good things often come if you keep asking questions. :))
