Going through older posts and noticed this one had not received a reply.
The LDS records actually show more than 9 children (extracted and submitted records):
Robert born 19 Apr.1855 Innishrush (s)
Samuel born 2 Dec.1856 Innishrush, died July 1940 (s)
Thomas born 1 May 1861 Innishrush (s)
Joseph Morrison born 20 July 1863 Innishrush (s)
James born 20 July 1865 Bellaghy district, Londonderry (extracted)
Mary born 14 Jan.1868 Innisrush (s)
Gerald Ballantine born 26 July 1870 Innishrush (s)
William Morrison born 6 Oct.1872 Innishrush (s)
David born 11 Apr.1875 Co.Londonderry (extracted)
Catherine born 11 Apr.1875 Co.Londonderry (extracted)- twin with David. You list a Catherine born 1877 Glasgow so it's likely this Catherine died before 1877.
The first complete census for Ireland is 1901 and 1911 is also available. National Archives, Dublin is gradually putting them both online- keep checking here under future plans to see when County Londonderry will be added:
www.census.nationalarchives.ie