Corrected sentence:
Sloths are nap champions. They sleep upside down on branches almost all day.
Why this is better (easy steps):
- Subject and verb: "Sloths" is plural, so we use "are." That is correct.
- Make short sentences: The original sentence is okay, but two short sentences are clearer for a young reader. So we split it into: "Sloths are nap champions." and "They sleep upside down on branches almost all day."
- Who does the action? "They" tells us that sloths do the sleeping. This makes the meaning very clear.
- Words meaning: "Upside down" means their bellies face the ground, and "almost all day" means they sleep most of the day.
If you want one sentence instead, this is also correct: "Sloths are nap champions, and they sleep upside down on branches almost all day."