No kids & save the dates

As long as it was addressed to just the parents and not “the smith family” then you should be fine. It can also be spread by word of mouth.

When you do your invites you can just make sure to list how many seats you're giving and to whom specifically

Also, you can include a note on the Wedding Website.
We are having an adults only, except the kids in wedding party, as it is in a Casino/Resort I am NOT the “bad guy”- and simply have a “We regret to inform you that due to our venue no one under the age of 18 is permitted to attend”... Best of Luck.

Do you have a website? You can also put it on there. When you send your invites out, make sure they are addressed to the first specifically. That way there is no confusion.

I think the invitation is the the place for more detailed information. Oftentimes people haven't planned that far for save the dates information so it's really not a problem to put the info on the invite.
Just be prepared for some No's on the rsvp list.

We are having a no kids ceremony and reception with the exception of our nephews who will be a part of the ceremony and likely leave after dinner. We didn’t put it on the save the dates but have been mentioning it word of mouth to friends and family that have kids. It will also be clearly stated in the invite that we ask only the adults attend. still trying to find the right wording for the invite though.

Make your intentions known when the invitations go out later. We're addressing the invitation to only the adults in the home, stating how many seats will be reserved for them on the RSVP, and adding it to our website's FAQ. We're also quietly starting to let it be known by word of mouth. Surprisingly most our friends are okay with no-kids; they're really looking forward to a night out.

I didn’t put it on our save the dates, but I DID mention it on our website, and the link was on the save the dates. So the information was out there, indirectly. I also started casually mentioning among family so it would spread out to my cousins who have a million kids each.

Do you have a website? I would add it to your website and spread it by word of mouth for now. Then add "Adult Only Affair" at the bottom of your invitation.

I would put it on your wedding website, and address the invites to parents only with an RSVP card specifying how many are invited.