According to "Lionel Trains, Standard of the World, 1900-1943" it is somewhat unclear when production started. The Lionel Corporation 1918, was successor to the Lionell Manufacturing Company. That company was granted patents as early as 1907 for train related items. Lionels numerical listing indicated catalog number #1 is for a Trolley, motor car 1906.
I will leave to experts to determine the earliest produced item.