If he (= the child) does something slightly unkind to a younger child, do the same to him at once. He will protest, and you can explain that if he does not want it done to him he must not do it to others. In this way the fact that others have feelings like his own is brought vividly to his attention.
Source: On Education, especially in early childhood, 1926, Pt. 2： Education of character, chap. 9: Punishment
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