Help finding my father's missing sibling

[Cumbrianangel]

On the 1911 census my grandma has stated that they'd had 6 live children, 5 living, 1 had died. I have searched and researched for a sibling born between their marriage in November 1901 (their first child was born February 1902) up to the census date but can't find a birth or death in either of the districts I know they would have been registered in.
A friend told me that they had a baby daughter in hospital in the '60's and the birth was never registered. Was this illegal? And surely you required a death certificate to bury a child?
Any help would be very much appreciated.
The parents were Jane (nee Owen) and John Henry WRIGHT who married in Bermondsey where their 1st 2 children were born (St. Luke's). They then had another 3 children when the moved to Belvedere Kent (Dartford).

[avm228]

Some people are likely to have included stillborn children in their 1911 fertility numbers, though those children would have had no birth or death registrations.  It is also likely that some children who died very soon after birth (so not stillborn) were not registered, even though technically they ought to have been.

[avm228]

Can you set out the family’s known dates (marriage, and the 5 known children)? It would make it easier to help you find a missing one.

[durhamgirl73]

Elsie Ethel 1902
John James Victor 1903
Leonard Hector 1905
Albert Henry 1906
Frank William 1909
Frederick Robert 1909

Are these the children?

[Cumbrianangel]

Yes they are Durhamgirl. Frederick Robert (my dad) and Frank William were twins.

[durhamgirl73]

Are one of the children listed missing from your research?

Leonard Hector died in 1906 OND Dartford 2a 338

[Cumbrianangel]

Yes! I blame it on the lateness of my post but I've just spotted Leonard Hector. Where was his birth registered?

[durhamgirl73]

Leonard Hector Wright 1905 AMJ Dartford 2a 594

[Cumbrianangel]

Thank you SO much. I will apply for a birth cert tomorrow and keep my fingers crossed. The fact I couldn't find the missing child has haunted me for ages. Poor grandma, my grandad died of TB aged just 42 in 1916 then Frank, my dads twin, died as the result of an accident on a bike aged 16. Times were very hard, grandma had to take in washing to make ends meet. Good night and thank you again 🙂