My first thought was to check if there are baptismal records for any children of Robert & Esther (or other Pentlands) which would give an indication of parents and date of birth (or at least baptism date).
However, I google the names of Eobert Pentland & Esther Sefton and came across this topic on another forum-
http://boards.ancestry.co.uk/thread.aspx?mv=flat&m=10178&p=localities.britisles.ireland.arm.general
The Will of Robert Pentland (mentioned in the above thread and covering 3 pages) is online- "Probate of the Will of Robert Pentland late of Mullabrack County Down Farmer who died 6 September 1897 granted at Belfast to George Clarke of Terryhogan County Armagh Farmer and Ann Pentland of Mullabrack Widow." and mentions son Joseph, etc.
http://applications.proni.gov.uk/DCAL_PRONI_WillsCalendar/WillsSearch.aspx
The notes I have suggest that Robert Pentland, bap 3 jun 1827, Tullylish, Down, son of John (and Hester) married for the first time to Anna McClelland Beatty. ( have no dates for their marriage. I believe this is the same Robert who died 6 sep 1897, Mullaghbrack.)
I also have a record for a Robert Pentland, had a wiife, Esther Sefton, married 4 oct 1850, Tullylish, Witnesses were William Sefton, and Francis Jones. Robert was from Mullaghbrack, and Essy was from Clare. Robert and Esther were having children at least through Jul 1868, when there is a record for the birth of their son, George Pentland, b. 11 jul 1868, Banbridge, Seapatrick.
If this is the same Robert who married Ann McClelland Beatty, it likely took place after 1868.
They had six children.
Joseph Pentland, b. 13 jan 1884, Armagh
John Pentland, b. 19 sep 1885, Lurgan, Armagh (some idea that his full name could be Sefton John Pentland - based on the death record of his wife Christina).
Rebecca Pentland, b. 6 may 1887, Lurgan
Alice Pentland, b. 11 dec 1888, Lurgan
Evelene/Eveline Pentland, b. 26 jul 1892, Armagh
Robert Pentland, b. 6 jan 1896, Armagh
Here is a census record for the above John and his wife Christina Miller
1891 Census, England, Yorkshire
John Pentland, b. 1853, age 38, b. Ireland, gardener
Christiana Pentland, b. 1859, 32, b Worcestershire
Christine Pentland, b. 1885, age 6, b Hampshire
Sefton Pentland, b. 1889, age 2, b. Hampshire
There is record Sefton Pentland, b. jul-sep 1888, New Forest, Hampshire, England.
Sefton Pentland can be found in the 1916 Canada Census, Medicine Hat, Alberta
Sefton Pentland, 26, b. England, English, farmer
Joanah Pentland, 24, b. USA, Norwegian
1921 Canada Census
Sefton Pentland, 33, b. England, parents b. England, emig 1910, farmer
Joehna Pentland, 33, b. USA, parents b. Norway, b. 1910
