• (n.) The quality of being puerile; puerility.
Pu'er·ile·ness noun The quality of being puerile; puerility. 
puerile, puerileness 1. Silly or immature, especially in a childish way. 2. Relating to or characteristic of childhood; such as, boyish, childish, juvenile, immature, trivial. 3. A reference to respiration which is characterized by the louder pulmonary murmur found in children, that in adults is usually a sign of disease.