The New Zealand BMD (at: https://www.bdmhistoricalrecords.dia.govt.nz/)
shows a number of children for George and Mary (Ann), including twins in 1900! There are no births for search later than 1913, but it's likely Mary and George continued having more children unless there was an unfortunate event. There is no guarantee these are the correct children nor that ALL of them are theirs from this record, but you could get the mother's maiden name if you ordered copies of the certificates. Expensive, but probably the only solution unless you make contact with a family member who already has the certificates. Good Luck!

Year/Reg# Surname Child Mother Father
1900/9772 White Henry Everet Mary George
1900/9773 White Hazeldine Mary George
1903/19657 White Stanley Mary George
1909/20319 White Norah Mary Mary George
1910/4225 White Margaret Kathleen Mary George
1911/6592 White Charlotte Margaret Mary Ann George
1912/27885 White Gladys Mary Mary Ann George

Thank you for your help. The last two are the ones I have already as their offspring. Charlotte was a spinster and Gladys has dropped off the search, I'm assumming she married but to find her married name is proving difficult.