Seated at your writing table and in the solitude in which God speaks to the heart, you should listen as a child listens and write as a child speaks. The child is simple and detached because he has yet no self-will, no pre-established positions, no artificial desires, no passions. His naïve confidence and direct speech have an immense interest for us. A mature man, enriched by experience, who should yet preserve this simplicity of the child would be an admirable repository of truth, and his voice would reecho in the souls of his fellow men.
If you are suspicious of Sertillanges' statements about the nature of the child, try to put aside as a "given" those self-centered attributes that all men possess by virtue of the Fall, and think only of the child's natural proclivities on the basis of his very limited knowledge and very open curiosity. The child does not ask or speak out on the basis of calculation of how it will affect his self-image or reputation. The child doesn't offer observations in order to garner support for an ideology. The child doesn't offer his own opinion in order to please others so as to be accepted in their company. He has no acquired tastes for which all of his words and actions are bent toward serving. It will not take a child long to learn each of these vices, but in his natural capacity they are harder for him to come by than the mature human soul. Therefore, the more the mature human soul can seek to recapture the relative innocence of the child's ability to speak from his plain and shameless ignorance, the more the mature human soul will be able to avoid the shamelessness of serving his refined, self-centered pretensions.