“I have managed to find 8 children. John Thomas 1865, James Ivan ( sometimes called James William) 1870, Robert 1871, Margaret Ann 1874 -1874, Sophia 1875 - 1877, Ellis 1878, Joseph 1880, and my grandmother Sarah Alice 1883 ( born after her father died) .”
I think ‘James Ivan’ is a transcription on 1881 census, unless you have him with that name elsewhere. He is registered and baptised as James William in 1869.
Is he also missing in 1871?