Grammar check for a 6-year-old: 'Big or small, islands are bits of land sitting in a sea of splashy water!'

Great sentence! It is grammatically correct and sounds fun.

1. Intro phrase: The opening words "Big or small," are an introductory phrase. The comma after them is correct because it separates that little start from the main idea.
2. Main idea: "Islands are bits of land" clearly says what an island is. The words are simple and fine for a 6-year-old.
3. Where they are: "sitting in a sea of splashy water" is a playful way to say islands are surrounded by water. That is okay, and it makes the sentence lively.
4. Punctuation: The exclamation mark (!) shows excitement and is fine to keep if you want the sentence to sound cheerful.

Two simple alternative ways to say the same thing:

• Big or small, islands are pieces of land surrounded by water.
• Big or small, islands are bits of land in the ocean.

Try reading your sentence out loud. If you want it more playful, keep "sea of splashy water!" If you want it more plain, use "surrounded by water." Either way, your original sentence is correct.