Corrected sentence: Shallow water may hide mud that can bog you down.
Why this is better — step by step for a 7-year-old:
- Start with a capital letter: Sentences need a big first letter. So write Shallow instead of shallow.
- Use water instead of waters: Both can be okay, but shallow water sounds more usual.
- Leave out the before mud: We are talking about mud in general, so mud (not the mud) fits better.
- Put a period at the end: Every sentence should end with a dot ..
- Meaning of bog you down: This is an idiom. It means to make you stuck or slow you down. Literally it can mean getting stuck in mud, and it can also mean something making a task harder.
Simple alternative (easier words): Shallow water can hide mud and make you stuck.
If you want, I can give more examples or help rewrite the sentence for a story or a safety sign.