I'm not sure specifically as there could be many 'old mill pond' stories. It might be about the history of a particular old mill pond, like the daily life around it in the old days, the people who worked at the mill, or some legends associated with the pond.
The moral could be about being content with what you have. The little frog has its small pond which might seem insignificant compared to bigger places, but it's still a home that provides all it needs.
I'm not sure specifically as there could be many interpretations. It might be about a baby named Thomas in a glade, perhaps with some sort of adventure or discovery in that setting.
Survival is a common theme. Since she's in the glade, she has to figure out how to find food, water, and shelter. Another theme is mystery. The glade itself is often portrayed as a place full of secrets. For example, there could be hidden passages or unknown powers.
The main characters are, without a doubt, the little frog and the small pond. The frog is the protagonist that we probably follow in the story. It may swim in the pond, sit on the lily pads in the pond. The small pond is the context within which the frog exists. It's the stage for the frog's activities, and it shapes the frog's life in the story.
One interesting plot could be the baby's discovery of a hidden path in the glade. It might lead to a magical place filled with strange creatures and beautiful flowers.
Obviously, Baby Thomas would be one of the main characters. But without more information, it's hard to say who else might be. There could be characters that are guardians or friends in the glade.
The secret of the pond in Qing Yu Nian's Taiping Courtyard was a place known as the Forbidden Door. This door could be a laboratory. There might be modern high-tech equipment inside, such as mobile phones, navigation, computers, and so on. The Forbidden Door involved the secret of the extinction of mankind and the origin of Ye Qingmei. However, the specific secret content was not explicitly mentioned in the search results provided.