Thank you both for your replies. Yes, they are the ones. And that daughter of 2 months old disappears in the 1871 Census.
You mean that she has died between censuses?
There are 18 deaths for Elizabeth Griffiths, between 1861 and 1865, in Merthyr Tydfil district.
In 1866, age at death was introduced.
So another possibility is:
March qtr 1867
Merthyr Tydfil district vol 11a, page 273
Elizabeth Griffiths age 6