I have been such a procrastinator. I have read a lot, but not made decisions, so I appeal to you. What are the best things to do for a day on each of these islands with a 50 year old, an 8 year old child, two 70+ year olds and an 85 year old senior. We can split up, so it can be two different things, but say which is best for 8 year old and which is best for 85 year old. No particular interests, except 8 year old loves beaches and one 70 year old has an interest in Lord Nelson.
St Lucia
Barbados
Antigua
St Thomas. Is Megan's beach the best bet for all?
Thanks for any opinions or ideas.

Sass: I gather you will be on a cruise?
On Antigua: Nelson's Dockyard! (Too bad you aren't going to Nevis, home of Fanny Nisbet, Lord Nelson's aggrieved widow!) It is full of interesting history that even the 8 year old might enjoy.
St Lucia also has British naval history. The cruise ships stop in the northern part of the island, where most of the interesting stuff (IMHO) is in the southern part.
Barbados: I enjoyed the wild eastern shore (Bathsheba), but I'll let others tell you about the rest.
St Thomas: Magens is great with a gentle entry and a shallow, sandy bottom. The beach kid will love running along the shore, building sand castles, etc. Usually a chance for interaction with local kids, too.

Esterenderusvi,
It is so nice to get opinions from a real person, not just brochures. Yes, a cruise this time. I wish we were gong to Nevis too, but we have our Granddaughter, one daughter and very senior friend with us. Our other daughter lives on St Kitts, and they have not been there, so they will be going to her house and she will take them around for the day. DH and I will be on our own, but keep Nevis for our own next visit. We have been several times and will go again soon, so can see Nevis then. We will see though. I am a huge history buff of Lord Nelson, have been to many places he went, the Battle of
Trafalgar area, visited his tomb, etc. Personally, in St Kitts though, I would just like to go to Ocen Terrace's pool for the day.

Should we rent a car in Barbados?

I would rent a car even if it is only for a couple of days. A trip on the windswept east coast is recommended, totally different vibe to the Platinum coast and you can visit places such as Harrison's cave that the 8 year might like and plantation houses such as Sunbury. You can't swim on the east coast BTW. Another nice thing to do if you are there on a Sunday is to go to the Gospel breakfast at the Crane hotel The location of the hotel is spectacular. It is popular so need prebooking.

In Antigua, the 8 year old might like a trip to see the sting rays. It's an easy excursion.The main historical attraction is Nelson's Dockyard and Shirley Heights above it.

In St Lucia I took my daughter when she was young on the Jolly Roger pirate ship trip.

" Should we rent a car in Barbados? "
I've actually only been to Barbados on a cruise. When we got off the ship (and after being directed through the shopping area) we ended up at the taxi stand. We told the dispatcher we wanted a tour for just the two of us. She called someone from the ranks, a delightful young lady. We said, "Show us the Barbados that will make us want to come back." We saw some historical sights, Bathsheba, had lunch at a local spot, drove across the northern section, Holetown, "the strip", and eventually back to the ship. She was a great guide and obviously loved her island. I try to avoid the bigger van trips which are regimented for cruise hordes.

(We enjoyed Greenwich when we were in London last year, especially all the Lord Nelson history like his coat.)

With a well thought out itinerary for the day , I think renting a car in Barbados could be quite fun . A trip to Saint Nicholas Abbey, round about the East coast , maybe lunch at Animal Flower Cave recently refurbished and views are so beautiful . Down the west to a nice beach for swimming and or a quick Jet Ski ride and back to the cruise ship, maybe