child: [OE] For a word of so central importance, child is surprisingly isolated, having no known living relatives in other Germanic languages. Its prehistoric Germanic ancestor has been reconstructed as *kiltham, which some have linked with Gothic kilthei ‘womb’ and even with Sanskrit jathara ‘belly’. The plural children is not an original feature; it developed in the 12th century. In earliest Old English times the plural was unchanged, like sheep.
