I'm going to post a list of reasons why I believe children don't belong at weddings, as they can add a significant cost to the overall event and spoil your day.
1. As said in the last post, a plate for a child (depending on your venue) can cost about $70 - $90. They won't eat it. You have 5-10 kids in attendance, there goes about $600 in the garbage.

3. If you allow one child, everyone is going expect to bring theirs. Your wedding becomes a day care centre. The parents (or whoever gets stuck babysitting) don't have a good time and don't get to spend time with you and they end up leaving early. The midnight buffet you had prepared for 150 guests is now serving 120 guests.
4. A new trend that is emerging is for those with children to encourage the couple to have a babysitter/day care on site. Guess what! That's expensive. No thanks.
5. Lets face it - some venues and events are just not suitable for children. Sharp edges on tables, a very expensive white dress in the room, sharp knives for dinner, an abundance of alcohol, etc...
6. Kids pick their noses and everything else. Kids stick their fingers in everything: food, cake, the chocolate fountain, etc... and give random surprise hugs! Those hugs and formal wear don't mix.

8. If you have children in your wedding party, they are most likely very close to you, and that's fine. However it can be very difficult to get your wedding photos taken with a screaming 3 year old and a miserable, hungry 6 year old. It can end up taking hours to get a few good pictures.
9. Again, if you have kids in the wedding party, some people will expect you to pay for the flower girl's dress or the ring bearer's suit/tux. Don't forget you need to get them flowers and a thank you gift as well.
10. Do you really want to have to spend time and money coming up with activities and games for children? And parents, it's a night out! Don't you want to enjoy yourself and let loose for once?

Again, all of these reasons are MY opinions. I personally cringe at the thought of a child in attendance, but some people love the idea of little ones running around hyped up on cake. However, I do have a fair reason to think this way. When I was 7 I was a flower girl for the 3rd time in my aunt and uncle's wedding. At the altar I got really sick, pale ghostly white and had to wear a hot pink sweater for the rest of the day because I was so cold. Everyone was worried about me, I ruined the pictures and there was vomit. Enough said.