Choosing an adults-only wedding is completely reasonable, and saying so is the part people get wrong. Say it too softly and guests bring children anyway; say it too bluntly and you spend the run-up to your wedding fielding hurt phone calls.
The wording matters more than the decision. Here's how to do it.
Where to say it
On the details card or your wedding website, never as the headline of the invitation. The invitation announces the wedding; the details card explains the day. 'Adults only' belongs in the explanation, not the announcement.
The same goes for the RSVP: addressing the invitation to the adults by name is the clearest signal of all. 'Mr and Mrs Smith' means Mr and Mrs Smith, not the Smiths plus two children.
The wording that works
Warm and clear beats clever: 'We love your children, but this one's a grown-up party.' Or 'Adults only, please, so everyone can let their hair down.' Or simply 'This is an adults-only celebration.'
Notice what none of those do: none apologise excessively, and none make it about anyone's specific children. State it once, warmly, and move on.
Handling the pushback
Someone will ask, and it's usually a relative. The answer is the same every time: 'We'd love to have them, but we've decided to keep it adults-only, and we've applied that to everyone.' The last half is the important one. Consistency is the only thing that makes the rule feel fair.
Making one exception is how you end up with one confused child at an otherwise adults-only wedding, and ten more relatives wondering why their children weren't the exception.
The exceptions worth making
Two are common and sensible. Babies in arms, because a breastfeeding mother and a two-week-old aren't really separable, and your own children or nieces and nephews in the wedding party. Both are understood, and both are consistent with the spirit of the rule rather than a hole in it.
If you want to go further, offer to help with childcare: a crèche in a side room, or a list of local sitters. It turns a 'no' into a 'we've thought about you', which is most of what the hurt is actually about.