In the 'big cat little cat story', it could be that the little cat is always trying to be as strong and brave as the big cat. The big cat has a majestic presence and the little cat admires it. They might have an adventure where they have to cross a big river. The big cat jumps across first to show it's safe, and then the little cat musters up the courage to follow.
We can learn about mentorship. Just as the big cat might teach the little cat, we can see the importance of an experienced figure guiding the younger or less experienced one.
Once, a big black cat befriended a little sister. They decided to explore the attic together. In the attic, they found old treasures like antique dolls and dusty books. The cat seemed to be very interested in the old leather - bound books as if it could read the stories inside them.
Well, I'm not sure exactly as I haven't read this specific story in detail. But generally, it might be about the little cat's adventure on or around the big red bus. Maybe the cat gets on the bus by accident and has all sorts of interesting encounters during the ride.
Once upon a time, there was a big cat in the yard. A little girl liked to tease it gently with a small feather. The cat would jump and pounce playfully in response.
The little pussy could have an interesting encounter with a mouse. Instead of chasing it right away, it might have just watched the mouse curiously for a while, as if trying to figure out what this little creature was doing in its territory.
The main character is surely the little cat. Since the story is named after it and it's likely the focus of the narrative. The big red bus is also very important, so it can be seen as a secondary main character. There might also be other characters like the bus driver, who could be a human or an animal. And there could be passengers on the bus too, which would also be characters in the story.
Big doesn't develop in a traditional sense of becoming a different character. But he does become more determined as his story progresses. He starts out just looking for Froggy, but as he realizes Froggy has the Chaos Emerald, he becomes more focused on getting it back.