A simple sentence is a sentence that consists of one independent clause. An independent clause is a clause that can stand alone as a sentence, which means that it contains all elements a sentence should contain. It has a subject and predicate and expresses a complete thought.
<em>The children wore their dirty boots. </em>is an example of a simple sentence. The complete subject is <em>the children,</em> and the complete predicate is <em>wore their dirty boots. </em>As we can see, this sentence makes sense, which means that it expresses a complete meaning.