Hi Lemmon,
Abervon according to my map is part of Neath, would the following be your family in 1851
1851 Census, Quan Neath, Glamorgan, Wales
Thomas Llewellyn, Head, Aged 48 Labourer, Widower
Mary Llewellyn, dau, aged 18
David Llewellyn, son, aged 12
Thomas Llewellyn, son, aged 8
Rees Llewellyn, son, aged 5
If this is your family, the mothers name is Eliza, there is also a child Catherine aged 5 in 1841 but not with the family in the 1851 census.
Kathy