Hilton Head, SC. Just within Sea Pines you get a few live music (kid appropriate or even tailored), tennis, riding, small animal farm, fishing, dolphin watch, gator watch, nature walks, lots of boating/touring options, plus amazing, wide beaches, lots of pools. For rainy days there's a children's museum very close and Savannah is about an hour away. We've been doing it with preschoolers for years and love it.

I've rented a condo beachside south of Clearwater and it worked out well. We were steps from the beach and pool, could drive to Clearwater Aquarium, restaurants and we went to Legoland one day too. It was inexpensive and family friendly (except for the strip clubs - oh Florida!).

Sarasota 16:01 is right lots of non-beach attractions, an urban core with an artsy flavor close to natural attractions like Myakka River (mild mannered alligator boat tour would be good with 4 year old.) Siesta Key is popular with families. Pineapple area downtown and St. Armand's Circle for dining out.

Underwhelming is kind of what people like about Captiva.
Omni on Amelia Island often sets up an inflatable slip-n-slide on the beach and their family pool is nice. Fernandina Beach has some cute shops and restaurants but it is pretty small , you could do it in three days.
Honestly I like the white sand and Caribbean water color better on the southwest coast.
Marco Island Marriott has really nice pools and landscaping. You can check out Naples or go on a dolphin watching tour.

Thanks, pp. That's exactly what I'm looking for. Will check out the vrbo listings. PP who recommended Captiva, it looks great for a couple but none of the activities you recommended are suitable for a four year old.

Sarasota, FL area - Lido Key, Longboat Key have great beaches. Fly into Tampa, drive 1 hr south.

Activities -
The Florida Aquarium – Tampa, FL
Lowry Zoo – Tampa, FL
Glazer Children’s Museum – Tampa, FL
Museum of Science and Industry – Tampa, FL
Lettuce Lake Park – Tampa, FL
Manatee Viewing Center – Apollo Beach, FL
Myakka River State Park – Sarasota, FL
Mote Aquarium – Sarasota, FL
Sarasota Jungle Gardens
G.WIZ - The Science Museum – Sarasota, FL
Circus Sarasota
Marie Selby Botanical Gardens – Sarasota, FL
The John and Mable Ringling Museum of Art – Sarasota, FL
Lido Beach – Sarasota, FL
Caspersen Beach - place to find shark's teeth - Venice, FL
Clearwater Marine Aquarium – Clearwater, FL
The Pier Aquarium – St. Petersburg, FL

The South Seas Island Resort in Captiva has it all:
pool, beach, plus you can rent a zillion different watercraft directly from the resort: kayaks, motor boats, catamarans, etc etc etc. A game room where you pay one price, and have the latest video games for an entire 24 hr period. Think arcade games which are large-sized. Plus the resort has a sailing school for kids, which they will love. Some of the best shelling in the US. Golf is right in the resort. So is tennis. You can charter a boat just outside the resort, but still on the island. Fishing from beach.

We are looking for a beach vacation destination for July that has a nice beach but also some other activities for a preschooler. I've been looking at Captiva, Sanibel, Gasparilla and Amelia Island and am worried that beach/pool won't be enough for our kid or us. We like the beach but we are not beach people per se. Discussions on here of Captiva, Sanibel and co have said that they are remote and underwhelming. Any other FL suggestions? We don't really know it well. Also, we will fly and likely rent a condo.