So, 3 of my kids play violin, one plays cello. A couple points:
-Learn to tune that shit yourself. Get an app on your phone, whatever. It needs to be tuned EVERY time it gets played. If you don't, there won't be consistency in where his fingers need to be to make an in tune sound. Tune it. Every time. Try the app Pano Tuner. Learn to use it so the strings are close to right every time. Did I mention every time? A little practice and it'll take less than a minute.
-Figure out how much tension need be on the bow, and relax it every time it's not in use. Every time.
-Use rosin regularly, and just as regularly clean it off the strings. Part of the reason kid violins are so scratchy and awful sounding is that the strings are covered with rosin.
-Strings don't need to be changed all that often. Perhaps 2 times a year if it's in high use. the type of strings you use matters, too. Research what's best for your violin. What size violin is it?
-Rather than buy, you can rent. Seriously, this is a good option. I use a company that allows all your rental dollars to accumulate. So as the kids grow, and you need different sizes, they swap them out and your rental dollars accumulate until you're at the point where your kid needs a full sized instrument. Then, all that money you spent renting goes toward the purchase price. Check them out:
Kenneth Stein Violins - Chicago Violin Shop
I have extensive experience with this. Ask more questions if you have them.