Im beginning to have doubts about the 1891 census, though cannot find anything better!
The reason being that in Jun 1881 both Sarah and Thomas are christened together on the same day, address Oswald Street. So the 1881 census is the right family, and Sarah and Thomas must be aged 3 and 5 when christened
IF the 1891 census is correct, then they would have Emma and John in 1881, and whilst they may not be on the census with them if staying with granny or whatever, one would have thought they would have been included in the family baptism. If they had been "done" as tiny babies, then you would have expected Sarah and Thomas to have been chr with them, if they suddenly realised they had not been chr.
Which child of Thomas and Emma are you descended from?