Thanks Dave more indication that they weren't married I suppose. It is complicated I don't think their children were aware they weren't married, at least they were always called Wood.

Helen,
The double registrations show up on FreeBMD. On Gro Index only the later registration of the two shows up.and in each case that is the Wood surname.
This means that at the time of birth Evelyn1920, Annie 1922, Doris 1925, Thomas 1932 and Kenneth W 1938 were each registered as Kirk and illegitimate.
At some date after 1938 they went back to the reg office to re register Annie, Doris, Thomas and Kenneth as Wood.For some reason not Evelyn.

You can purchase online the Annie Wood certificate digital image for only £2.50, and that will give you the date of that re registration. The others are less than 100 yrs old so would cost you a full pPer cert.
Dave