Perhaps he was at some point but the census record I found said coal miner in 1901. If we are even talking about the same family.
It seems fairly certain that not only is it the same family and that there were several other children you might not know about. If David and Mary Jane were alive in 1911 then it would be worth getting that census record to see how many children she had and how many were still living,
We've started with this family in the 1901 census in Scotland-
Robert, age 45, Coal Miner, born c1856 Ireland
Mary J., age 42, wife, born c1859, Ireland
John, age 22, Coal Miner, born c1879, Ireland
Robert E., age 19, Coal Miner, born c1882 Old Monkland
James, age 16, Tile Work Labourer, born c1885, Old Monkland
Joshua, age 14, Tile Work Labourer, born c1887, Old Monkland
Ann Jane, age 13, Scholar, born c1888, Ireland
David, age 11, Scholar, born c1890, Ireland
Nellie, age 10, Scholar, born c1891, Ireland
Minnie, age 10, Scholar, born c1891, Ireland
Sarah, age 8, Scholar, born c1893, Ireland
Some of the Irish births have been found already but here's a more complete list- all born Armagh, father- Kirkland, mother Cullen:
Margaret Kirkland born 25 June 1879
Extract:
https://familysearch.org/ark:/61903/1:1:FGJ3-P59Ann Jane Kirkland born 30 Dec.1887 at Markethill, Armagh. Father- weaver
David Kirkland born 6 June 1889 at Richhill Parish, Armagh, address was Ballyloughan. Father- weaver
Eleanor Kirkland born 26 Apr.1891 (Nellie)
Mary Kirkland born 26 Apr.1891 (Minnie)
Sarah Kirkland born 8 Feb.1893
Samuel Kirkland born 14 Oct.1898