Oh, thank you all so much. David was born on 2 August 1906, from what we know. I do not have any documents or census, as I have absolutely no idea how or where to begin.
Mum's mum, (mum also Agnes) died following the flu. Her dad, David, left her and her 2 siblings with their maternal grandmother, and he provided for them for about 5 years, and then everything stopped. No money, no visits, no information.
Til the day she died, Mum always wondered what happened to her "daddy". She would never speak of him or her mother, and neither would her cousins whom she was brought up with. I know back then there was "children should not ask questions," so I guess they never did because neither her sisters, Margaret or Caroline, knew anything about him either. They did say they had a brother called John who died just before his mum as an infant.
Any help towards finding out would be so much appreciated. More than you can ever imagine.