Thank you both for your help - the trouble is I can find John and James in Scotland in 1881, 1891 and 1901, but there is no record of Thomas after his birth certificate in 1875. In 1881 he would only have been 6, so I would expect him to be at home with his parents. I had another look on SP last night but still haven't found a death certificate between 1875 and 1881 for a 5-6 year old boy. It's difficult to believe that a boys death wouldn't have been recorded around that time, they weren't exactly living in the wilds. The certificate may be misnamed, and I just haven't found it. The other thing that occurred to me was that he may have been living with another family member, possibly with his mother's family, but he should still have showed up on the census somewhere. Unless he's recorded with a nickname, not Thomas - I've tried Tom, Thom and Thos, and T*, not sure what else to try. The funny thing is there are no other Thomases in the family - the naming follows the Scottish convention and every family has almost the same names, in different orders. If I didn't have his birth certificate with his parents names and marriage date/place I would think he wasn't part of the family.