The purpose of a wedding is not to set the invites according to who can and cannot come. You invite who you WANT to be there and if they cannot come, for WHATEVER reason, they won't be there. No big deal.
I cannot agree with you more about a childless wedding. I feel like to be spending thousands of dollars (regardless who is shelling out the cash), weddings should be an adult affair. Children do not know what is going on and you are right, their presence totally changes the entire dynamics of any event. Kids get restless. Kids cannot sit in a chair for 4 hours at the reception. They will gather and cause a ruckus, as children commonly do. This is not to disrespect children or their parents, it is to RESPECT your event and the manner in which you want to conduct your wedding day.
Regardless of what children do not eat, the per plate is the exact same, unless on the odd chance they provide a children's plate accordingly priced. But, even still, children will get weary and antsy as they get overstimulated and skip their nap times.
You are two years out on this wedding, so you have plenty of time to address this situation with your fiancé. I understand his desire to invite everyone, but realistically, he is just clueless how children change an event, especially a wedding. I suppose if you wanted a family affair shindig, it would be okay, but you don't.
Whenever we were invited to a wedding, I ALWAYS left my children home with a sitter. The last thing I wanted was to be a parent and not enjoy ADULTS and adult conversation at the wedding. Besides, if alcohol is served, that is no place for kids anyway.
I have been to dozens of cocktail parties and events at friend's homes. Children are not invited so adults can gather and be adults, not parents. I invited 130 adults to my wedding. If everyone brought their children, I would not have only had to change my dream venue location, I would have had to increase the guest list to almost 175. That is quite a bit of money to spend to have children change my idea of an adult wedding day. I would never be upset if my children were not invited to a wedding. I would see it as an opportunity to spend some adult time with my spouse.
So, how do you convince your groom to leave kids out of your wedding day? Maybe go to youtube.com and see if you can find some wedding receptions where children were present and others where they were not. That will show, undoubtedly, the difference in atmosphere. Good luck to you.