Trivia: Mrs. Brisby's eldest daughter was voiced by a young Shannen Doherty, later to become famous for her role as Brenda in "Beverly Hills 90210."
Trivia: The main character, Mrs. Brisby, is called Mrs. Frisby in the book the based the film. The name Mrs. Brisby had to be used because the trademark for the toy "Frisbee" was taken.
Answer: Mrs. Brisby tells Nicodemus that Jonathan had been teaching her to read and her children as well. The children were better at reading that she was but that might be something that they inherited from their father. I think Mr. Ages was also able to read so that makes him intelligent as well. Remember the injections that the mice and rats were given also gave them the ability to read.