Beach/Island ideas for a kid that loves to wade in calm seas looking for sealife

Hey all, I’m looking for vacation suggestions for a Caribbean island (not Cancun—we just did that) where we could either find a great resort or easily do a rental villa where my 10-year old can spend a lot of time at a calm, walkable, beach. Open to pacific side Mexico too but I know I’m in r/Caribbean. 🙂

For example, last year we had a day trip to a small island and man-made lagoon while in Nassau and she was content to spend the entire day in the water, waist/chest deep spotting little fish while we swam slightly deeper or sat on the beach (bonus points if it’s gently shaded with trees). No crashing waves to worry about.

Some non-beach day activities are totally fine too, but beaches are a must (i.e. I loved Dominica, thought about Belize, but they rank lower on the “good beaches metric”). Turks and Caicos might be too pricy for us…

Any ideas? Thanks for the help!