Hi Auzzy,
Do you have William Henry John's birth certificate? If not, would be worth getting as it will confirm his mother's full name and help with pinning down his parent's marriage. Have you looked at the original image on the 1911 census to check that the surname does appear to be written as Johns, rather than just on the transcript? Are they at an address in 1911 that you know is linked to the family?
Ermy