Great sentence! It's almost perfect for a 6-year-old. Here is a tiny improvement and a simple explanation so you can understand why.
Original: Little cubs learn to roar like their big lion dad.
Small fix: The little cubs learn to roar like their big lion dad.
Why this is good:
- "The little cubs" tells who we mean. Adding "The" makes the sentence sound complete.
- "learn" is the action and it matches the plural word "cubs" (more than one cub).
- "to roar" says what they are learning.
- "like their big lion dad" shows they are trying to roar the same way as their daddy lion.
Extra notes:
- You can also say: The little cubs are learning to roar like their big lion dad. That tells us the cubs are doing it right now.
- Another simple version: Little cubs learn to roar.
Nice work — keep writing and practicing!