Most decent-sized MO shuls have some type of groups to keep the kids occupied during shabbos morning davening. I had always thought these groups were a good thing until I read a blog post a while back that questioned why we are so quick to evict kids from the main shul. Proper chinuch, the post argued, dictates that we use shul as another opportunity to educate our children. Instead many kids grow up thinking that shul is a daycare center or playground and don't get the opportunity to witness and emulate their parents' devotional activities. (Granted that the quality of both the groups and parents' behavior in shul varies widely and it isn't easy to make blanket statements.)
I've always taken David to shul with me on shabbos morning ever since he was little baby. Everyone always marveled at how well behaved he was, certainly better than many of the adults. Recently it's been harder to get him to stay in shul with me for the entire davening. (Yes, I'm aware that the fact that such a state existed to begin with was rather abnormal.) This is probably due to the fact that as he gets older he simply doesn't want to sit in the same place, even if he has an ample supply of books and toys. Also, there are now a few children in the shul and he probably wonders why they get to run around but he has to stay with me. In any case, for the last few months the understanding has been that he sits at my side and does his davening. Then he can read a book or play with some toys in his seat. Along the way he may ask me some questions about what is going on or otherwise I will point out some things to him. At some point he gets to go out and play with the kids and then comes back in for anim zmiros.
Recently I've been trying to help organize groups for the kids in my shul. This is something I've wanted to do a for a little while, but it has become more important for me now that David is in public school. Following up on the idea (here) that I want to make sure he has a solid anchor in the Jewish community, I want the shul to have a nice group of Jewish kids for him to associate with and I want the shul to be a positive Jewish experience for him in general.
I still wonder if maybe he really does belong in the shul at my side, but I hope we can run reasonably well organized groups that will serve him better than sitting at my side. The worst case scenario, however, is if the groups take off, but are poorly run and become nothing more than a babysitting service. At that point I think I'd prefer he sit with me in shul, but I then I'd be competing with the groups.