I don't know why they were in Wales, but there is also the following
1881
RG11/5288
4 Hewill Street, Cogan, Penarth
Thomas Sampson 34 Boot maker b. Penzance
Matilda 27 Middlesex
Thomas 7 Canada, Hamilton
Evelyn 4 Glamorgan, Grangetown
Beatrice 2 Glamorgan, Cogan
Ada E 3 months Glamorgan, Cogan
1881 Wales census
Mary, widow, is with daughter Fanny Frost and family, again in Penarth. Final column mentions she is blind from birth
So it looks as if most of the family moved there
