Plewsy on this link you were also sure another of your 
CARLEN ancestor had emigrated to Australia but was found in the US.
http://www.rootschat.com/forum/index.php?topic=654848.0Is this your family in 1851?  If so, mother appears to be 
Susan not Sarah.
1851 Census  HO107/1537/178/ 41
Living at  82 Nichol Square, Shoreditch [There was also another family living at this address]
CARLEN Thomas Head Married 60 years Merchant's clerk  Born South Shields
CARLEN Susan Wife Married 50 years  Born Hampton
CARLEN Thomas Carlen Son 6 years    Born Mid City Rd
MORGAN Catharine Servant 15 years   House Servant  Born Westminster
Oh Neil I now see Neil has mentioned the 1851 census however I have listed Thomas' seniors occupation so will leave it.
This may be Susan's death
Deaths Mar 1868  
CARLEN Susannah    67 years    Islington    1b/144
Incidentally do you have Thomas's birth certificate?  If not how do you know you have the correct Thomas?
Cando