One of the featured characters in "The Snowmen" was Captain Latimer, father of Francesca and Digby.
The story took place in 1892, approximately. So I'm thinking it's pozz'ble, just pozz'ble, that the Captain remarried a few years after the events of the Christmas special and had another son, named Timothy. Timothy was sent away to the Farringham School for Boys in the Norfolk area and had his own encounter with the Doctor in 1913.
If for some reason this theory of "relateeveety" doesn't work, it could still be that Tim was the nephew of Captain Latimer.