Albert is registered in O/N/D 1895 in Ledbury district
Wilfred Christopher is J/F/M 1898 in Tenbury district
That narrows the gap a bit!
There are no Wanklyn's from O/N/D 1896 to O/N/D 1897 in either of these areas.
Again, either they moved somewhere else in these years, or your missing babe is not in this gap either.
They seem to move a lot - are you SURE all 17 are the same family?

!!
I suggest that next you do go through year by year and find the registration of each child, and look for a possible twin that did not survive. This can be done for free on Ancestry, though the indexing is sometimes off and you have to use some imagination (I found, on one quarter I had to key in Walton and then scroll on to Wanklyn, for example)
Will be interested to hear if you find him/her eventually, but I must go. People tell me there are other things to do in life other than Rootschat!