I have the My First Number Train set, pictured here. This set did not come with track. Other sets, such as My First Train set, pictured here, do come with track, but the wheels look different. Can this kind of track fit the My First Number Train set? Or is there a different kind of track that can be used with the My First Number Train set?
Not really - the wheels on "My First Number Train" are the DUPLO car wheels, so they will just about fit on straight and curved track, but they won't work on the points and bridge sections.
There isn't any track designed for the wheels in "My First Number Train", that's just designed to pulled around on the floor.
You can just about see a chassis in this picture - they are about to crash at the points: