Children typically use smaller string instruments than adults. Violins are made in so-called fractional sizes for young students: Apart from full-size (4/4) violins, 7/8, 3/4, 1/2, 1/4, 1/8, 1/10, 1/16, 1/32 and even 1/64-sized instruments exist, although these smaller sizes are highly unusual and usually custom-made. Extremely small sizes were developed, along with the Suzuki program, for violin students as young as 3. Finely made fractional sized violins, especially smaller than 1/2 size, are extremely rare or non-existent. Such small instruments are typically intended for beginners needing a rugged violin, and whose rudimentary technique does not justify the expense of a more carefully made one. While related in some sense to the dimensions of the instruments, the fractional sizes are not intended to be literal descriptions of relative proportions. For example, a 3/4-sized instrument is not three-quarters the length of a full size instrument. The body length (not including the neck) of a full-size, or 4/4, violin is 356 mm (about 14 inches), smaller in some 17th-century models. A 3/4 violin's body length is 335 mm (about 13 inches), and a 1/2 size is 310 mm (about 12 inches). With the violin's closest family member, the viola, size is specified as body length in inches or centimeters rather than fractional sizes. A full-size viola averages 16 inches (40 cm). Occasionally, an adult with a small frame may use a so-called 7/8 size violin instead of a full-size instrument. Sometimes called a lady's violin, these instruments are slightly shorter than a full size violin, but tend to be high-quality instruments capable of producing a sound that is comparable to that of fine full size violins. I don't know the correct answer and since I am an adult I use the 4/4 size without any problems. I believe the choice of violin size depends on the age and physical condition of the child. If the child is young and small start with half size violin and so on until the child grows and can handle bigger violins. The problem is if the child grows rapidly, the smaller violins will become useless. Consult with the music teacher. The above is the reference from Wikipedia.