If Nellie was born in 1892, she is unlikely to be having children after 1936 in the US. Presumably they would have been born in Antwerp or in the UK
There are several Griffiths children with mother's maiden name of Chambers registered in England or Wales between 1924 and 1936 but most are unlikely ( ie there are also Griffiths/Chambers children registered prior to 1924 in the same reg district) There is one possible registered in Wakefield in 1931.
I haven't checked the UK births overseas register on Find my Past.
BUT, do you have a reference for the marriage date?
I ask because I couldn't find a marriage in London (or elsewhere) for a Percy Griffiths and a Nellie Chambers in 1924.
There is one for Percy L T Griffiths and Nellie Chambers in the first quarter of 1936.
GRO INDEX Wandsworth Surrey 1d 717.
There is also a marriage between Percy Lionel T Griffiths and Eleanor Edith Hayward in Rochford (reg district in Essex) 3Quarter 1909
(All info from search at freebmd https://www.freebmd.org.uk/cgi/search.pl
The 1911 census finds this couple with no children . He aged 26; a clerk, bank agent born Barford St Mark, Salisbury, Wiltshire. She aged 25, born Kenninghall Norfolk. They They had been married 1 year and had no children.They were living at 37 Glengarry Road. E Dulwich. (PRO RG 14,piece 2473 , Camberwell,
South London image viewed on Ancestry UK. (But shorter transcript available at family search)
Unfortunately its not going to be easy to find when Eleanor died. (Several possibles) .