Here we have a truck:
It has a steering wheel, wheels on either side (cushions), bricks in the back, and a CD player so that the driver doesn't get bored on long journeys. Ian is non-descript cargo.
This (note how it is totally different!!!), is a tractor:
It's key features are small wheels (2) at the front (stickle-bricks), large wheels at the back (tiger feet), a steering wheel, and a sheep (Ian) in the trailer. What, you didn't identify the animal from the face it's pulling?!!
There is also a train, which has no steering wheel, but has two different levers, a funnel, two carriages and passengers.
All are made up of a stool and two chairs, but the exact arrangement of the furniture is key. Woe betide the parent who puts them in the wrong place - "No Dadddy - that's a truck. Making a tractor now!".