Unique etiquette question. Nursing moms with older children.

I don't think it's rude or odd to have only nursing infants and having the older kids at a babysitter. The nursing infant exception is a safety amendment to the rule as the baby needs to stay with mom to be healthy and happy.

We more or less did the opposite with my sister's wedding because her two oldest were big enough to sit down for dinner but her twins were infants so she sent them to a sitter for the reception and not the two older kids.

As someone who also comes from a large family (30+ first cousins. Oof.) I understand lol. We chose to have all kids of all ages because this was too difficult to navigate (plus it was just easier for us!) but I definitely see your perspective here! I don't think it would be rude at all, since as you said - the nursing infants are the exception to the rule. I think allowing the wee-babes who are still nursing to attend is a great move on your part. As long as it's clear that it's an adults only affair, it should be well received that this is the exception and not a special "allowance," you know? Will some of them still push for the others to come? Sure. Will some of them be mad or decide not to come? It's possible. But it's your event, and you have decided you don't want all the kids there, but have been generous enough (and have the common sense) to grant an exception. Stick to your guns, girl!

If you are uncomfortable telling people they can't bring their children, other than the ones nursing to the reception....does your venue have an extra room that you could hire a babysitter? The kids not nursing could be at the ceremony but go to the babysitter for the reception. Granted your reception isn't going until really late but in that case, I would assume that those nursing would probably be leaving early anyway. Up to you but I do think that you should have the reception you want. Allow the nursing babies but not the older kids.