The state, condition, or quality of being a child; childhood or childishness.
From 'child' + '-ness' (suffix forming abstract nouns). This is a somewhat archaic or rare formation; modern English prefers 'childhood' to 'childness,' though the '-ness' suffix could theoretically be applied to 'child.'
While 'childness' is theoretically valid English, nobody really uses it—we have 'childhood' for the state and 'childishness' for the behavior, showing how English often chooses or creates specific words rather than using productive suffixes in all possible combinations.
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