I wouldn't think such prose possible of such an age, either, but remember, children of 200 years ago---who were educated---were educated in letters and math to a FAR greater degree (given what they could be taught) than today. I've seen a state of NJ high school ENTRANCE test from 1891 that would stagger most college graduates.
The intelligence of children is very underestimated. My mother came from a brit colony where everyone of a certain primary school age had to learn latin for church. Do you know of any government school teaching elementary school kids latin? I don't.