In case the stuff at family search isn't seeable (I can't see it)—First marriage: John O'Brien Spouse: Annie Moloney marriage date: 08/10/1873
Ann O'Brien birth date: 24/10/1874
Catherine O'Brien birth date: 14/09/1876
Mary O'Brien birth date: 14/02/1879
Margaret Theresa O'Brien birth date: 14/11/1881 death date: 16/08/1885
Probably(?) the same Catherine that was born in 1876: Catherine Gertrude O'Brien death date: 08/05/1926, Mother: Annie A. Maloney, Father/parent: John Thomas O'Brien
I’m not finding a fifth child for that marriage, nor death dates (name is too common to match for marriages) for Ann or Mary, unless Ann is also Annie: Annie Teresa O'Brien death date: 15/01/1876, Mother: Ann Malone, Father/parent: John O'Brien
Second marriage: John O'Brien Spouse: Catherine Reid marriage date: 19/11/1885
Thomas Francis O'Brien birth date: 23/09/1886 death date: 18/04/1888
John Henry Percy O'Brien birth date: 21/06/1888 death date: 03/08/1968
IF he did do a runner, so to speak, after the death of the elder boy, it doesn't have to mean he left the area. It may be that he just walked out on his pregnant wife and stayed somewhere in the area because of the business. (It is something that, sadly, still happens today. A child dies and, instead of the parents drawing closer, the marriage just falls apart.)