Generally speaking, children have to take the value of their mental work on the faith of our word.

They must go through a great deal in mastering the rudiments of, say, Latin grammar (for the honey is not yet spread so thickly over this as it is now over the elements of modern languages).
They must wonder why "grown-ups" have such an infatuation for things that seem out of place and inappropriate in life as they consider it worth living.

Probably it is on this account that so many artificial rewards and inducements have had to be brought in to sustain their efforts.

Physical exercise is a joy to healthy children, but it leaves nothing behind as a result.

Children are proud of what they have done and made themselves.