I played violin and am teaching my daughter violin, so here's so more info for you:
I would say a middle-class family would actually purchase a violin assuming their child was very interested. A used violin can be purchased for $250-700 and a new one can also be found within that range. There are student-quality violins and professional-quality violins. The professional quality run from anywhere in the high hundreds to more than most people make in a year. Strings are very affordable, in the $3-10 range, depending on brand. They're tough, but an eager student can break one by overtuning. The most likely to break is the E string, the thinnest of the four. Unless the string is decades (maybe centuries?) old or the player is beyond vigorous and is beating up the instrument, it will NOT break during play.
Rosin is hardened sap. It looks like amber and breaks into a white powder. It comes in a little rectangular block (about 1.5" by 3") or a circular block. The hairs of the bow are drawn across the rosin to gain an application of the powder. The powder helps the bow "stick" to the strings as the bow is drawn across them. Most people use the frog of the bow (the little metal piece on the end you hold) to scratch up the block of rosin before using. The bow hairs are tightened by twisting the frog before playing - until they are "taut" but not "tight" and are loosened again before storing. The bow is stored in the top of the violin case, under the lid.
The violin sits under the left side of the chin and the player should be able to hold the violin there without any other help - just by using the chin and shoulder. For many this is difficult due to thinness of violin and length of neck, so there are contraptions called "shoulder rests" available. The shoulder rests are a padded sort of stand that attaches to the underside of the violin and rests on the shoulder. Google it for a picture. Some bypass the shoulder rest and instead use a piece of thick foam under the violin, securing it onto the violin with a rubber band.
The left wrist of the hand holding the violin must always be dropped. It is one of the first and perhaps one of the most difficult things to learn.
There are four strings on the violin - G, D, A and E with G being the lowest and E being the highest. It takes time to learn how to properly tune the strings, so a teacher would likely do it for the first year or so (sometimes more). There are two ways to tune a string. At the tip of the violin are four tuners that look like pegs. They are turned to do "major" tuning. Closer to the bridge (the little wooden piece by where the bow in played) are the fine tuners. They look like little screws and perform a finer pitch tuning.
Posture is very important when playing. The musician sits with a straight back on the edge of the chair. Feet are on the floor, shoulders are back, and the right elbow is high.
A band is wood, brass, wind, percussion instruments. An orchestra is all string instruments. That is the division in school, however, if a band and an orchestra are combined it is called an orchestra. In high school we did occasionally combine.
Sadly, many schools are cutting music budgets and the orchestra tends to be the first to go. In my area of the Puget Sound, WA, we started in 5th grade. Some kids had private lessons, as well. There are two kinds: Suzuki and Classical. Google them for more info. In my opinion, the best education is a blend of the two. It is possible, with small violins, for children as young as 3 to begin learning to play. During a concert, musicians are expected to wear all black or black and white. A first-violin is the most talented member of the orchestra and has auditioned to gain that spot. It can be lost. There is sometimes competition and/or jealousy about who gets chosen ("They weren't THAT good . . ." etc). The first violin often gets chances to play solos in orchestral pieces.
As for schools, I would say that violinists tend to go vie for great music schools once they get to looking at college. Julliard, of course, is one of the best. Even so, there are lots of opportunity to be a part of an elite organization in high school. There are audition-only youth orchestras sponsored by major city orchestras, high profile audition-only music camps, festivals, institutes and chamber groups in the U.S. and international. The best players spend their summers at these.
Hope this helps!