Childishness is a related term of silliness.
In uncountable|lang=en terms the difference between childishness and silliness
is that childishness is (uncountable) the state or characteristic of being childish while silliness is (uncountable) that which is perceived as silly or frivolous.
In countable|lang=en terms the difference between childishness and silliness
is that childishness is (countable) childish behaviour while silliness is (countable) an act that is silly; a result of being silly.
As nouns the difference between childishness and silliness
is that childishness is (uncountable) the state or characteristic of being childish while silliness is (uncountable) that which is perceived as silly or frivolous.
childishness
English
Noun
(uncountable) The state or characteristic of being childish.
(countable) Childish behaviour.
See also
* puerilism
* puerility
silliness
English
Noun
(uncountable) That which is perceived as silly or frivolous.
(countable) An act that is silly; a result of being silly.