We decided we are not inviting children to our wedding either. For us, it is mostly a money thing. We are paying for our own wedding and I can't see spending so much money for a child. I know you can get children's dinners but I'm not about to pay $30 for mac and cheese.
Also, some of the children that would be invited (ie - my neice and nephews) are a bit unruly and obnoxious when the attention is not focused on them. I've had to deal with that at other family affairs and I choose not to deal with it at our wedding.
We had a cousin of my DF ask if children were invited. We told her the only children that would be there are our Jr. Bridesmaid (who is our daughter), our ringbearer and there were 2 younger cousins invited (11 and 9) because their parents are going through a rough divorce and since it's Christmas time, we figured we'd let their folks decide if they should come or not.
Anyway, everyone knows about the rule and hasn't complained about it. My DF's one cousin is bringing a babysitter with them who is a friend and they are making a vacation out of the rest of the time.
They know we are paying for everything ourselves and haven't complained. I did have a cousin of mine ask if her son could come. THey've never been to Disney and she'd like to take him, but she has no place to leave him. He's 13 and the quietest boy I've ever met, so we said yes.
You really just need to use your own discretion. Do what you feel is right. Most of the times I've been to a wedding with children, it's been fine. THere have been times when the children get out of hand and their parents are nowhere to be found, but as someone else said, just make your coordinator aware of those situations and she/he should take care of it so you don't have to.
Most importantly, enjoy your day!!!