Hi
Is it this family?
1861 census RG9 328 folio 52
14 Eltham Street St George Southwark
James Benfield 31 Head Married Coal dealer Poplar Middlesex
Susan Benfield 35 Wife Married Blackfriars Surrey
Thomas Childs 16 Son Floor cloth printer's boy Blackfriars Surrey
Elizabeth Childs 14 Daughter Blackfriars Surrey
William Childs 12 Son Blackfriars Surrey
Susan Childs 10 Daughter Blackfriars Surrey
Emma Childs 8 Daughter Blackfriars Surrey
Matilda Childs 5 Daughter Blackfriars Surrey
Mary Benfield 10 Months Daughter Blackfriars Surrey
Have you obtained a copy of Matilda's birth certificate (or her baptism if that is not found)? Does it state her father was still alive at the time of her birth/baptism? If her birth wasn't registered and the other children were, it may indicate the family was facing some sort of difficulties at the time.
If he was that would narrow down the possible window of his death between Matilda's birth and her mother's remarriage in the first quarter of 1860. Or if not between Matilda's birth and Emma's birth.
Thomas' death should be registered in the registration district it took place in. If he didn't die in Southwark near his home, his death might be registered by someone who did not know him well. Since he was a relatively young man if his death was by unnatural causes, in an accident for instance it would be registered by a Cororner after an inquest. Thomas could have been visiting friends or relatives. He could have died near his workplace which might be across the Thames, or be in an institution. All good reasons which might make his death registration so much harder to find particularly since the other quite a few Thomas Child/s death registrations around this period.
If he was buried locally the cemetery records to check first would probably be Nunhead which opened in 1840.
http://www.southwark.gov.uk/YourServices/BirthsDeathsMarriages/cemeteries/nunheadcemetery.htmlRegards
Valda