I took my kids to my cousins wedding 2 years ago, at the time they were 2 & almost 5, the wedding was small & I know my kids. 1st of all, I took a coloring book for each & each had their own crayons (no sharing/fighting) also, I sat on the back row so I could walk out if I needed to. Much to my surprise, my kids sat the entire time without making a peep & actually watched the service. Like I said, I know my kids and they have been taught from early on that there is a time & place for everything & church is no time for play, fighting, whining, etc.
They were both in a wedding June 5, DS just turned 7 & DD 4, they did great!! They stood through the entire ceremony & never made a sound & did not need to be the center of attention. DD did wave to me once during, but that was all.
So, I guess to answer the question as to whether or not kids should be, is up to the bride & groom. Some couples now have someone in the nursery to keep kids, I did this for DD when she was 8 mo. old (my kids were invited to the wedding, which was out of town), I don't think I would take an infant otherwise to a wedding. If the kids are not invited, however, I don't think you should take them.