On the other hand, parental affection, when it is of the right sort, undoubtedly furthers a child's development. Children whose mothers do not feel a warm affection for them are apt to be thin and nervous, and sometimes they develop such faults as kleptomania. The affection of parents makes infants feel safe in this dangerous world, and gives them boldness in experimentation and in exploration of their environment. It is necessary to a child's mental life to feel himself the object of warm affection, for he is instinctively aware of his helplessness, and of his need of a protection which only affection can ensure.
Source: Bertrand Russell :Marriage and Morals, 1929
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