One of the characteristics that makes the Violin a great starter instrument is that it comes in a broad variety of sizes, some of them especially designed for young students.
VIOLIN SIZES FOR KIDS AND ADULTS
There are 8 main sizes, with each corresponding to the length of the body of the violin (not including the neck and scroll): The smallest is 1/16 (9 inches). It is followed by the progressively larger sizes of 1/10, 1/8, 1/4, 1/2, 3/4, 7/8 and finally 4/4 or full size (c. 14 inches).
As you can see, there really is a size for everyone! And for young beginners, it is understood that when they grow out of their violin size, they move up to the next larger size. Incidentally, small student violins can be purchased at very reasonable cost, and when your child moves up to the next size, you may be able to trade it in, or of course, sell it in pre-owned condition on the internet.
Another advantage of choosing the violin for young beginners is the relatively low weight of the violin. This is a consideration for transport and equally important, for (daily) practice. Violinists do carry their instrument on their bodies when performing, and having less to carry is always a plus.