Source : Webster's Revised Unabridged Dictionary (1913)

Puerility \Pu`er*il"i*ty\, n.; pl. {Puerilities}. [L.
   puerilitas: cf. F. pu['e]rilit['e].]
   1. The quality of being puerile; childishness; puerileness.
      --Sir T. Browne.

   2. That which is puerile or childish; especially, an
      expression which is flat, insipid, or silly.

Source : WordNet®

puerility
     n 1: the state of a child between infancy and adolescence [syn: {childhood}]
     2: a property characteristic of a child [syn: {childishness}]