Charles Waring Darwin, who died when he was 18 months old (6 December 1856 – 28 June 1858), was the last of the children of Charles Darwin and Emma Darwin, their tenth child and sixth son. He was born and died at the family home of Down House in Kent.[1]

It was noted by Henrietta, in her biography of her mother, that the child was born "without the full share of intelligence". Darwin noted that even though "he was backward in talking & walking" he was nevertheless "intelligent & observant". These descriptions of his development, combined with his mother's advanced age at the time of his birth are consistent with Down's syndrome.[2]

Darwin already feared that the consanguinity of his and Emma's lineage — she was his first cousin — had contributed to his children's constitutional weakness, a fear that would find its expression in The Origin of Species in which Darwin rails against the "evil" effects of inbreeding and lauds the good effects of crossing.

Charles Waring succumbed to scarlet fever and died at the age of about 18 months.[1] Darwin wrote in his personal 'journal', "June 28 Poor dear Baby died."[3]

The baby's illness and early death kept Darwin from attending the first publication of Darwin's theory at the joint reading of papers by Alfred Russel Wallace and himself titled On the Tendency of Species to form Varieties; and on the Perpetuation of Varieties and Species by Natural Means of Selection at the meeting of the Linnean Society on 1 July 1858.
https://www.findagrave.com/memorial/91914405/charles_waring_darwin