What is it you want? It's difficult to just "come across" a family but we could help try to find some facts for you.
William was 33 born Hoddesdon in 1861 and Susanna was 35 born Notts Sutton upon Trent. They already had children Elizabeth 9 born Hoddesdon, William 7, John 5 and Richard 2 the other children born Ware.
Do you need 1871 information? which we can find a lot more easily with their dates of birth and birthplaces.
They lived in Fairbrother's Yard, St Andrew, Hertfordshire
William Felstead Head M 44 Draper's Porter Herts Hoddesdon
Susannah Wife M 46 Notts Burton on Trent
Richard Son 12 Herts Ware
Katherine daur 8 " Hertford
RG10/1373 Hertford Folio 15 Page 25
I would think this is William in 1851, judging by his age and birthplace
Lords Lane, Hoddesdon, Hertfordshire
Thomas and Sarah Shipton have a lodger
William Felstead U 24 Groom Herts Hoddesdon
HO107/1705 Ware Hoddesdon Folio 58 Page 25
If you were able to give the information from the 1881 census as fully detailed as these above, we could also help to see if we can find them in 1891 and 1901 if you don't have that already.
Now we have his date of birth and place, somebody might be able to do you a 1841 census look up, I wonder if he could still be with his parents then?