We went to Beaches Turks & Caicos several years ago with another couple. We did NOT take children and had a wonderful time. We found that on the first full day of most people's arrival (Sunday) they'd keep their children out in the sun all day - oddly enough - we rarely saw the children after that. (Guess they were all in the infirmary with sunburn!)
Beaches CAN be for adults - you just have to know how to plan your days. If you are a pool dweller, rather than a beach bunny - keep in mind that most of the kids (and parents of said children) are in the pool. Many of the restaurants there are adults only all the time or at least after a certain time. Plan for a late dinner - if you're going to go to eat at 6 pm - you'll be inundated by children.
We hit the Carribbean every March and we try to never stay at the same place twice. We've hit Beach T&C 3 times in 4 years! We absolutely love it there - the staff is superb, food is good, premium drinks, no tipping and beautiful beaches! ^