Based on my experiences of churches…
Yes. Well, some do. Most show up on time/early. A very few will be there within 5 minutes of the start time. A very, very few show up later than that.
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It depends from church to church. Generally, the ushers will not allow people in during prayer (as it will disturb others) and sometimes there are specific places in the service where they don’t seat people - however, there’s leeway based on whether there are seats that can be accessed without disturbing anyone, how long and well the late person knows the usher, etc.
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For the most part, no. Occasionally whispers between people, but generally, people don’t talk to each other more than is necessary (exception, teenagers - somewhere there will be a cluster of teenagers together in one section, and they do whisper to each other, and pass notes, and do other teenager type things. However, they’ll be generally quiet about it, and try and not disturb those around them. They’ll fail at this - but within 3 pews of them, things are generally normal.)
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No. But then, almost every church I’ve been in has had a nursery, so almost anything older than a newborn to about kindergarten age isn’t in service anyway. The parents of the very smallest tend to sit in the back, with their babies and remove the infants once they start to get cranky. Young elementary school kids (and some times all elementary school kids) are usually either not in the service at all - or escorted out shortly before the sermon to activities that are more age appropriate for them.
I have seen children loaded down with stuff (books, drawing paper, crayons, etc. to keep them seated and quiet) but the closest I’ve ever seen to running around is the occasional toddler who stands on the pew to see what’s happening behind him/her. When the parent catches her, she’s generally sat back down and distracted reasonably quietly.
Dress has gone from more traditional (my dad wouldn’t allow us to wear anything but dresses and skirts to church - my friends were allowed to wear nice pants and pantsuits and short suits, but still dressed up) to now where in many churches, dress has gone to more and more casual (I now wear jeans. I very, very occasionally miss dressing for church - but not often - Easter, I’ll dress).
stargazer - I think I know your church (I grew up in one of the Covenant churches on the eastside), I love that building. Rest of demographic info - 28, Seattle area, now attending a presbyterian church.