The Collaborative International Dictionary of English v.0.48:

Childhood \Child"hood\ (ch[imac]ld"h[oo^]d), n. [AS. cildh[=a]d;
   cild child + -h[=a]d. See Child, and -hood.]
   1. The state of being a child; the time in which persons are
      children; the condition or time from infancy to puberty.
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            I have walked before you from my childhood. --1.
                                                  Sam. xii. 2.
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   2. Children, taken collectively. [R.]
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            The well-governed childhood of this realm. --Sir. W.
                                                  Scott.
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   3. The commencement; the first period.
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            The childhood of our joy.             --Shak.
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   Second childhood, the state of being feeble and incapable
      from old age.
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WordNet (r) 3.0 (2006):

second childhood
    n 1: mental infirmity as a consequence of old age; sometimes
         shown by foolish infatuations [syn: dotage, second
         childhood, senility]