Hi Ray,
I think William and Mary had two children (possibly more) Nora c1907 and Hilda c 1910.
Best to start with what you know for sure and work backwards, once you get back to before 1911 it should become easier as you can access the censuses 1841-1911 on a site like Ancestry or Findmypast.
www.freebmd.org.uk is free and very useful for finding members of your family although not quite up to more recent dates yet.
Bear in mind that we ve all sent for wrong certificates before

especially with a common surname.
Freebmd will give you a reference and year and quarter which you can use to obtain bmd certificates from 1837 from
www.gro.gov.uk , i think they are about £9 each.
www.familysearch.org is free to use with records mainly before 1900.
It is exciting and very addictive!
Lots of help available on Rootschat, especially if you re stuck, just ask.
Best wishes
Cathy