Can I jump in here - I would not worry about Thomas having said he had 4 children and one alive. Sometimes they did not really understand the question. My GGM said she had 8 children born and 8 alive - I have birth certificates for ELEVEN and deaths for three before 1911 so the info she gave was wrong - it should have been 11 children and 8 alive.
I was very interested in this post as I had actually adopted Thomasina into my family and now have to chuck her out - reason I adopted her was this - an Agnes Robinson my great grandfather's cousin is on 1911 census at
http://census.nationalarchives.ie/pages/1911/Antrim/Court_Ward/Wellwyne_Street/150161/She has a daughter Thomasena Robinson with her aged 3 - and only Thomasina on births was the one in 1907 - you know all about her.- Agnes also had a brother Thomas whom I had not been able to find. Also her father was James who was a CARPENTER. All my lot jelled with info on your lot. When I got the birth for Thomasena and then the Thomas Robinson/ Sarah Service marriage and his dad was James a carpenter I thought the Thomasena with Agnes was her niece not her daughter - Just goes to show there can be massive co-incidences when you have a common name like Robinson.