How to for Parents: When is your child ready for music
That was a tough one for us when we were getting ready to get D and Dv set up with their instruments. Even $350 is a lot to pay for a cello that might not be played! And the piano! Well, with tuning every six months, let’s just say it felt like quite a risk. Upon reflection, it’s a risk I’m definately glad we took - for both kids - but we also let them lead us. These instruments were their chosen instruments rather than some decree coming from a parent, grandparent, or aunt. 
However, if you’re wondering what to do and when to do it, take a look at this article. It should give you a little better understanding of the what, wherefores, and whys.