Q:

What was the source for Adam's children in the endnotes to Josephus' "The Antiquities of the Jews"?

I was reading Josephus' account of Adam's children in "The Antiquities of the Jews" (located in Book 1, Chapter 2) and noticed that the total number of children that Adam had was not in the text itself, but in the endnotes of the text. Where do these endnotes find their origins?
I specifically am interesting in the origins of this endnote:

"The number of Adam's children, as says the old tradition was thirty-three sons, and twenty-three daughters."

A:

The footnotes on this (and other editions of Josephus) seem to be referring to pages in A Collection of Authentick Records Belonging to the Old and New Testament by William Whiston.
In this case, another online version offers this particular footnote with the reference thus:

(11) The number of Adam’s children, as says the old tradition, was thirty three sons, and twenty three daughters, in Authent. Rec. Part I. pag. 454, 457, 469.

On page 454 of Authentick Sources, we read that:

and on page 457 we see:

William Whiston, M.A. produced one of the earliest (possibly the earliest) translations of Josephus into English. The references in the footnotes thus link into another of his translations of "biblical" records.
Copies of the works by the Byzantine scholars Syncellus and Cedrenus mentioned by Whiston are available on archive.org (although the only copies that I found are in Greek), if you are interested in taking your research further.

