Amana, while I totally agree with you about the church scenario, understand that the masjid set up is different. It's more social, less formal and hence the comfort zone the kids have there. Yes, children should be exposed to the masjid but there is a time for that. My daughters go the masjid for Islamic studies and now understand the etiquettes of being in that environment but before that as much as they tried, they couldn't keep to themselves when they saw their friends there. See in churches the have benches and no one has to get up for the entire durations of the sermons and prayer (I've studied in catholic schools all my life) but at the masjid, ladies sit on the carpet in circles during khutbas and when they get up for namaz, they gather up at the lines leaving all the kids to do hanky panky at the back :D
^ True, the set up is less formal, but perhaps since I grew up going to church I was easily able to adapt that attitude towards attending the masjid. My children have been praying next to me (or at least going through the motions) since they were about 18 months, so we have never had major problems. I think a lot of the problem is the culture norms of not insisting that small children behave, or even of not taking them to the masjid while they are small.