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:
Yes, the number train will fit on the "My First Train Set" track. But only because it doesn't include any points, crossings or bridges.
The duplo track generally guides the wheels from the inside; the insides of the wheels are the same distance apart on both trains. However the number train wheels are wider (the same as many other duplo vehicles) and won't fit through sections of track that aren't just straight or simple curves.
You can see from the picture that the wheels work fine, but overhang the sides of the track.