feeding off ev's post with the birthdates, here they are in the 1871 census:
11 Marlow Street, Govan
John is 34 and a Seaman
Jane is 35, the first clue I think we have to her birth year, born in England
Children:
Henry 14, Robert 12, Mary 10, John 8, Walter 6.
The elder 3 were born in England, John and Walter in Glasgow
(sadly just realised no record of William)
added: and here's the family in 1861 with an English address:
They are in the West Derby area of Lancashire, at No. 31 Kensington or possible Kissington(?)
Jane is 26 and the Head of the Household. She lists herself as 'Seaman's wife', born in Liverpool
John Henry is 4, Robert Nilson (sic) is 3, Mary Nilson is 3 months, and there is a 15 year old Servant, Rose Whalagg or Whabagg, from Dublin, Ireland.
(I think Rose's entry isthe first time I've seen the place in Ireland specified, I wish that same enumerator had taken the details for some of my relatives)
RG9/ 2731/ 86 p 16;
The interesting thing is that Neilson appears for both Robert and Mary, even though mis-spelled on the form, but for Henry he is listed as John Henry. He's 4, and 10 years later Henry is shown as 14, so it's not the sad case of one child dying and their using the name again, it has to be the same boy. So if ever you search for Henry's birth of any reason, he may be listed as John.