Can be confusedchildish childlike (see synonym study at the current entry)
Examples from the Web for childishness
And as a purveyor of childishness myself, I understand how annoying it can be.
Looking at the roots of larp makes the hobby easier to take seriously and divorces the desire from childishness.
At which childishness the smile on Ellis's face became broad, and he went away.The Barrier|Allen French
At times his hate grew too heavy for him, and he could have cried for relief in admitting his childishness to some one.Narcissus|Evelyn Scott
Her hair hung down her back in a braid, which gave a distinct touch of childishness to her.Other Main-Travelled Roads|Hamlin Garland
Such is childishness, however: I pitied the poor rhinoceros his "dull."Memoirs of a Midget|Walter de la Mare
Durham didn't know what to make of this old judge—sometimes he seemed simple-minded to the point of childishness almost.Back Home|Irvin S. Cobb