Trying to find the name of a movie?

I saw a movie as a child, but can't remember the name. I believe it took place in England, at least the actors accents sounded English. The movie was about a small girl who lived in a mansion in the countryside. There was a pond or a small lake on the grounds and she would go sit by it. At some point she came to find that there were living things in the lake...which were cartoons. I can't remember the entire plot, but I do specifically remember the girl and the cartoons referencing Thomas Aquinas many times. I loved this movie as a small child and would love to find the name and see it again if possible. Thanks for any help!