Practical spiritism, as we shall see more clearly the more we know of it, demands our utmost tact and discretion to avoid being taken in by deceitful spirits ; if grown people are in danger of being deceived by these, children and young persons are evidently, on account of their inexperience, still more exposed to this danger.
We know, too, that concentration of thought and feeling is absolutely necessary for obtaining the concentration of serious and benevolent spirits. An evocation made rightly and jokingly is a profanation which gives easy access to mocking and maleficent spirits; and as we cannot expect a child to possess the seriousness necessary for such an act, it is to be feared that he would make a mere amusement of it if left to himself.
Even under the most favorable conditions, it is highly desirable that a child who is endowed with the medianimic faculty should only exercise it under the eyes of experienced persons, who may inspire him, by their example, with the sentiment of respect that should always preside at the evocation of souls who have quitted the earthly life. The question of age, as I have said, is subordinate to conditions of temperament as well as of character; and you should not only avoid forcing the development of this faculty in children, where it is not spontaneous, but its exercise, in every case, should be conducted with very great circumspection, and should neither be excited nor encouraged even on the part of grown persons, if they are weak in body or in mind. Those who show the slightest symptoms of mental eccentricity or weakness should be dissuaded from its exercise by every possible means; for there is, in such persons, an evident predisposition to insanity, which any and every species of excitement would tend to develop. Spiritist ideas are not more likely to produce cerebral excitement than any others; but madness brought on by spiritist ideas would take its character from them, just as it would assume the character of religious mania, if it had been brought on by the excitement attendant on an excess of devotional practices, and spiritism, in such cases, would naturally, though unjustly, be held responsible for that result.
The best thing to be done, with every one who shows a tendency to fall under the influence of a fixed idea, is to direct his attention to something altogether different from that idea, so as to give rest to the organs which are the seat of the excitement (See Introduction to The Spirits’ Book, Par. 12.)
From The Medium´s Book by Allan Kardec, Chapter XIX