childishness

From Middle English childishnes, childisnes, equivalent to childish +‎ -ness.

childishness (countable and uncountable, plural childishnesses)

1. (uncountable) The state or characteristic of being childish.
2. (countable) Childish behaviour.
   • 1868, John Mockett Cramp, Baptist History: from the foundation of the Christian church to the close of the eighteenth century, page 43:

     Exorcism, unction, the sign of the cross, holy water, infant-communion, and many other childishnesses, were also called "Apostolic institutions" — not at first, but long after they were invented, to conceal their real origin […]

• puerilism
• puerility