If the children are

Thomas 1815
Harriet 1820
Sarah 1823
Eliza 1825
John 1826
Sally 1828
James 1830
Charlotte 1836 : christened 1836 - Newarne

I think this is the family on the 1841 census for Lydney (Newarne)

John COX - 55
Sally - 55
Sally - 13 (c1828)
James - 8 (c1830)
Charlot - 5 (c1836)

Just above John COX is Mary COX - 20

John COX baptised in Lydney 1790- parents John & Martha

John c1826 is on the 1841 census in Lydney (labourer) with Martha COX age 70 (his possible grandmother)

1851 Census Lydney

Same COX family, all born Lydney

John - 60
Sally - 60 (who appears to be called Sarah on the children's baptisms)
John - 24
James - 21
Charlotte - 15

(if you use the Advanced Search) - you will find a John COX (residence Newherne) and Harriet HOWARD (is she Harriet Cox c1820) witnesses at the marriage of William COX - (father John COX) to Caroline WARREN - 18 March 1852)