My understanding is that a CA Supreme Court ruling established that hotels which can be booked by the public can't restrict children from staying. I guess you can still advertise as adults only, but they'd be exposing themselves to likely civil suits by turning away guests with children. I've seen people say "what about the clothing optional pools" -- as far as I know it's not illegal for children to see people nude when parents are opting in to the possibility. I assume staff make sure they know.

I've heard of people getting pretty generous points comp when complaining about children being present at Ventana and Napa, but be aware it's entirely possible for children to be there despite the website's promise.