Institutio Oratoria

Just as small children suffer less damage from their frequent falls, from their crawling on hands and knees and, a little later, from their incessant play and their running about from morn till eve, because they are so light in weight and have so little to carry, even so their minds are less susceptible of fatigue, because their activity calls for less effort and application to study demands no exertion of their own, since they are merely so much plastic material to be moulded by the teacher.

And further owing to the general pliability of childhood, they follow their instructors with greater simplicity and without attempting to measure their own progress: for as yet they do not even appreciate the nature of their work. Finally, as I have often noticed, the senses are less affected by mere hard work than they are by hard thinking.