Archaic or dialectal possessive form meaning 'of a child' or 'belonging to a young person,' or plural of childe.
From 'childe' (medieval term for a youth of noble birth) + '-s' plural, or from 'child' in older English where possessives used '-s. This reflects the archaic grammar of Middle English before modern possessive forms solidified.
The form 'childes' appears in medieval texts and shows how English once marked possession differently—what we'd now say 'the child's toy' would have been 'the childes toy,' a remnant of a richer inflectional system English has mostly lost.
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