""It WAS Harold Williamson and was a section on Esther Rantzen's That's Life if I remember correctly."" - Yes; that's the one for sure.
There's a good obituary - he died in 2001 in the Telegraph:-
http://www.telegraph.co.uk/news/obituaries/1326250/Harold-Williamson.html
Children Talking started on radio, then moved to TV on Bradens Week in 1968, later becoming That's Life. Co-incidentally he started in TV on Man Alive, a Desmond Wilcox programme (later to become Esther Rantzen's husband!) I should have known as he was a County Durham lad like myself, and like me a keen Sunderland fan.
Thanks for all contributions!