My birthday is July 26th; I started kindergarten at 5, on schedule, and didn't skip at all. No pre-school. My mom tells me that she'd taught me how to read at home by age 3. I was vaguely bored for most of grammar school (Catholic), but the nuns generally let me grab a book off the shelf whenever I was done with my work, and that kept me occupied enough. It probably helped that I was a relatively quiet type back then. When I came home from school, I either went outside to play, often alone, or went up to my room to read, and was pretty content either way.
Kavi has a May birthday, so will be a little young for her class; Anand has a September one, which I think means he'll just miss the cut-off, and will be quite old for his class. They're almost 4 and 1.5 now, so these decisions aren't quite with us yet, but coming.
I suspect we're just going to go along with the standard schedule, though. Everything I've read suggests that trying to game the system by holding them back or pushing them forward has unpredictable results -- maybe helpful, maybe not, and impossible to tell in advance. If they end up being so bored that they have behavior problems, then we'll have to revisit this, of course.
I just hope the teachers let them read when they're bored. We moved to Oak Park for the excellent public schools -- hopefully they're as good as everyone says they are. And while we're not planning to do any kind of formal homeschooling, we certainly teach them things at home already, and will likely continue to do so. Kev and I work at home so much; the kids are going to get plenty of face time with their professor parents. Which may just make the problem worse, if they're far ahead of their peers at school. But I gather that there's an unusually high concentration of parents holding advanced degrees in Oak Park; maybe that will translate to a reasonable cohort of bright kids for them to hang with at school.
I don't really think it takes that much for a bright kid to be happy at school -- a few good friends, an understanding and flexible teacher. It doesn't seem too much to hope for.
Of course, they're still so young, we don't even know if they're going to be bright at all! So we may have nothing to worry about. :-)