The Name
The "N" refers to the number 9. The tracks for these small scale model railroads are only 9 cm apart.
Popularity
This is the second most popular size for model railroad layouts after HO. It is the not the smallest layout, as that would fall to the Z scale.
Scenery and Train Cars
HO model trains will have the most tracks, parts and accessories available for them, but as the second most popular layout, N scale train enthusiasts have plenty of options available for their hobby.
Considerations
The train scale is determined by personal preference and the amount of space available. If a new hobbyist does not have much space to work with, these smaller trains may be exactly what he needs.
Children
N scale trains are not recommended for younger children, and electric trains themselves are not recommended for children younger than six years old. These trains, however, are fine for the preteen or teenager taking up model railroading as a hobby.