findmypast shows a Raymond Lampkins dob 1915 travelling from Liverpool to Halifax, Canada, in 1923.
However, he was accompanied by Fred Geo 1877 and Rebecca 1879.
Could these possibly be relations of Ivy who took him in?
They were in fact Frederick George Lampkin and Rebecca Carter who married in 1895 in Milton reg dist.
His birth was registered in 1871 in Milton. (I see Mark you have him in your tree at gr, born in 1870, but no one else has him.)
Their household in 1911 in Folkestone was Frederick Lampkin aged 40, wife Rebecca aged 38, daughter Ivy aged 14. She was Ivy Edith, birth reg 1896 in Rye.
And Ivy E Lampkin married Jean Brivio in early 1915 -- the same quarter as the birth of Raymond B Brivio.
I think we have found her surviving child, who was in fact Raymond, as Mark said. He travelled to Canada as Raymond Lampkin(s) with his grandparents Frederick and Rebecca Lampkin.
I don't subscribe to findmypast to check the accuracy of the transcription and the other details, so maybe someone else can?
Dave's post was a very long time ago; I wonder whether a PM would reach him. (I've sent one.)
edit - I found a very old posting of Dave's at genforum (November 2000) and tried emailing him at the email address given there, but my message has bounced back as recipient address rejected.