I did some work on the children's death dates and I couldn't find any obituaries in any of the Dufferin County newspapers. The museum has the Orangeville Sun and Shelburne Economist indexed, and I went through the Shelburne Free Press for the dates and no articles.
In one of the articles you referenced in your previous response, it indicated John Smith's death occurred at lot 27 con 4 Amaranth. So I went through the property records for this lot today at the museum. It was an interesting exercise and it will give you lots to work on. I didn't write down all the property transactions that involved John SMITH, there was only one transaction that will give you some leads to work on.
In 1882 Eliza COLGAN (Plaintiff) of Osprey Township, wife of George COLGAN got a court judgement for partitioning or sale of lot 27 con 4 of Amaranth. The defendants were: James SMITH, Elizabeth WILLIAMS, Maria BOWLER, Matilda SMITH, Jane HALL, John HALL, William HALL, Thomas Smith, John SMITH, Mary SMITH, Jane SMITH, Annie SMITH (it was noted the last 5 were < 21 years of age).
The defendants named are the heirs of John SMITH (brothers, sisters, nieces or nephews) and Eliza (SMITH) COLGAN proved her case to be included in this list. I believe this does give you the proof that Eliza (SMITH) COLGAN is a sister of John, James and William, so that would make her a daughter of Thomas SMITH.
With William SMITH dying in 1880, it makes sense that the last five people mentioned in the list are his children. Excluding James SMITH who is the first person mentioned in the list, I believe the remaining people are part of a HALL family. For HALL family members to be included in this list, it only makes sense if Thomas SMITH had a daughter who married a HALL and this daughter had died before 1882. These HALL children would then be a niece or nephew of John SMITH.
Now the big question: Is the William and Mary HALL living next door to the SMITH family (1851 census) actually William HALL and Mary SMITH (another daughter of Thomas)? They are parents' of a Matilda HALL from the census and the parents' of Matilda HALL who married James SMITH, were William & Mary. Does that mean James SMITH married his niece Matilda HALL? This would explain why a Matilda SMITH is in the defendants' list as an heir of John SMITH. She would not be there as the spouse of James SMITH, but as a niece of John SMITH. Interesting?