The length of a sentence isn't what makes it hard to understand- it's how long you have to wait for a phrase to be completed. When you're reading a sentence, you don't understand it word by word ...

New research shows that a child's ability to regulate behavior—an aspect of executive function—is closely tied to how they understand and learn language.

This is the simplest type of sentence and is usually very easy to understand. Short simple sentences are frequently used to offer facts, so that they are easily understood by a reader. For example ...

These are very common when speaking and they are not difficult to understand. One advantage of compound sentences is that a writer can build more detail into their writing. However, one problem is ...