When something is ‘shallow’, it means it’s not very deep. Imagine a puddle on the ground after it rains. You can splash around in it without getting your shoes soaked because the water isn’t very deep. It’s just a thin layer of water, so we call it shallow.
Think of a sandbox at the playground. If you only put a little bit of sand in it, you can see the bottom easily because there’s not much sand. That’s what shallow means — there’s not a lot of something, like water or sand, from the top to the bottom.
Now, picture a book with only a few pages. You can read it really quickly because it doesn’t have a lot of pages to go through. This book would be considered shallow because it doesn’t take long to get from the beginning to the end.
Finally, imagine a swimming pool. If the pool is shallow, you can stand in it and your head will stay above the water. It’s safe for little kids because there’s not a lot of water to cover them. Shallow means there’s just a little bit from top to bottom.