If the above is the correct family here's a little more information:
(Had written this before your reply but still think it relevant)
Henry McDaid = Ellen O'Donnell 30/01/1876 Clonmany RC Church,(Henry was McDevitt on marriage record but McDaid in children's birth records)
Living at "Rockstown" for the birth of son John McDaid 1878, Rockstown I can see in old maps was in the next townland to Letter, Kinnea, Clonmany Parish, other births I have for the couple are James 1876,Bridget 1881 and Mary 1887.
It appears Rockstown is better known as Roxtown
I think this has to be the family (no other suitable family in the area)
Regards
Joe
One other thing if the families situation had taken a turn for the worst in the 1880's then some children may not have been registered as registration cost money, big gap between birth in 1881 and birth in 1887