Hmmm,
just wondering if you have the right couple in London?
You probably have good evidence for the London life of John and Amelia but there are a couple of other NEWMANs in London at around the same time.
There was another John NEWMAN with a wife Amelia having children baptised at St Pancras in the later 1850s, and yet another couple who seem to have similar names.
The John NEWMAN 30, porter (as he is living at the same address as a railway porter perhaps he is also on the railways) and Amelia 24 that you have in the 1851 census show John as being born in Wiltshire, Amelia in Aston Oxfordshire.
1861 census shows a John NEWMAN 43, Carman,
b Wiltshire and Amelia 34, b Brighton, living in Shoreditch with children 8, 6 and 1, the two older ones born in Shoreditch.
This chap's occupation is given as 'carman' (Carmen were often employed by railway companies for local deliveries and collections of goods and parcels. Also sometimes someone who drove horse-drawn trams was called a Carman.
http://rmhh.co.uk/occup/c.html)
Aston, Oxfordshire is part of Bampton which could be mis-heard by the enumerator as 'Brighton'.
The other couple are John Frederick NEWMAN and Amelia Adelaide still in St Pancras district in 1861.
I just wonder if one of these couples may be the ones in the 1851 census?
Edit to add:Have just read RebeccaClaire's post and I think her information is well worth considering. My thoughts are that the couple in St Pancras in 1851 may be the couple in Shoreditch in 1861 which, obviously, can't be your John and Amelia.
Judith