"Regarding Otto Simon Henry Harcourt, son of George Harcourt and Gertrude Lucas, have you ever come across confirmation as to Ottos childrens names, its his sons I need to trace."
Hello Brooke
Using
https://www.freebmd.org.uk/cgi/search.pl
Otto Simon Henry Harcourt was born 1849 in the Registration District of Eton.
Otto Simon H Harcourt, married 1872 in the Registration District of Swansea.
Otto S H Harcourt, Married 1910 in the Registration District of Westminster.
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Newspaper Births
You may wish to check the index for free by signing into the GRO Index, as there may be more possibles.
https://www.gro.gov.uk/gro/content/certificates/
The Standard, 15 October 1874
BIRTHS
HARCOURT.- Sept. 7, at Athens, the wife of Otto Harcourt, Esq., of a son.
No name, but birth Athens.
The Morning Post (London), 27 August 1875
HARCOURT.- On the 24th inst., at Broadstairs, Kent, the [wife? scan unreadable / missing] Otto Harcourt, of a son.
Possibly Wilfred Otto HARCOURT, Registration District of Thanet.
London Evening Standard, 26 November 1877
BIRTHS.
HARCOURT.- Nov. 18, at 101, Randolph-road, Maida-hill, the wife of Otto Harcourt, Esq., of a son.
Possibly Norman HARCOURT, Registration District of Kensington?
I can't access any Census images, but hopefully, somebody on here will be able to check the family in the Census for you?
Regards Mark
Hello Brooke
1871 Census (image not checked)
St George, Hanover Square, Middlesex
Otto Harcourt, Lodger, age 22, Unmarried, Engineer, Birthplace Wraysbury, Buckinghamshire.
Cyril Harcourt, Lodger, age 20, Unmarried, Medical Student, Birthplace Ryde, Isle of Wight.
1891 Census from Family Search (original image not seen / checked)
De Grey Road, Emmanuel, Leeds
Otto S H Harcourt, Head, Married, age 42, Engineer, Birthplace Buckinghamshire.
Isabella L Harcourt, Wife, Married, age 37, Birthplace South America.
Beatrice M. Harcourt, Daughter, age 18, Birthplace England.
Gerald St J Harcourt, Son, age 9, Birthplace Yorkshire.
Ivor J Harcourt, Son, age 6, Birthplace Lancashire.
Isabella Turner, Servant, age 21, Birthplace Northumberland.
Annie W Wain, Servant, age 22, Birthplace Yorkshire.
Christening (image not checked)
2nd June 1880
Clifton, St Paul, Gloucestershire
Florence Helena Harcourt
Father's Name, Otto Simon Henry Harcourt
Mother's Name, Isabella Leonora Harcourt
Regards Mark
EDIT, a very broad search (results also have conflicting/poor transcriptions):-
https://familysearch.org/search/record/results?count=20&query=%2Bsurname%3AHarcourt~%20%2Bbirth_year%3A1872-1910~%20%2Bfather_givenname%3AOtto~%20%2Bfather_surname%3AHarcourt~%20%2Bmother_givenname%3AIsabella~%20%2Brecord_country%3AEngland