We had five children ages 4-7 in the wedding party for my S and DIL. Their inclusion was totally the couple’s decision and they stayed for part of the party, as well. There were also 3 couples who had breast-feeding infants and the B & G encouraged them to come, as well. Two of those couples participated in readings or blessings during the ceremony and brought the babies up with them - my S and his bride smiled some of their biggest smiles during those moments. When one of those babies started to fuss during the rest of the ceremony they were swiftly carried to a place where they could not be heard. It was as the couple wanted…which, in my opinion, is all that matters!
I can’t imagine having no kids at a wedding, but I totally get that this is a personal thing. I love kids and think that weddings are family affairs, but I have been to several weddings where kids would have been out of place. We didn’t choose to do it that way for our daughter (even the rogue flower girl was funny to me), but I can see how some parents of young kids would really appreciate having the time to get a sitter and not have to worry about how their kids behaved.