Here are the corrected sentences and short, simple explanations for a 6-year-old.
Corrected sentences:
- Beavers make lodges from branches. The entrance is always hidden underwater.
- A beaver's lodge is made of branches and covered with clay. The entrance is always hidden underwater.
- Beavers build lodges in the water from twigs and clay.
Why these changes?
- Sentence 1 was already correct. You can keep the two short sentences or join them with "and" if you want one sentence.
- In sentence 2, "A beaver's lodge" is fine for one lodge. We use "made of" (common for what something is made from) and "covered with clay" sounds natural. "Safely" is okay but not needed—"hidden underwater" already tells us it is safe.
- In sentence 3, moving "in the water" before "from twigs and clay" makes it clearer that the lodge is built in the water, not that the clay is in the water.
Short version for you: All three talk about the same idea. Any of these corrected sentences are good and easy to understand.