"Mom, I want to be a trumpet player."I clearly remember the day I heard the words. Our son was nine years old, and so far in his young life his interest in playing an instrument consisted of banging on our piano about five minutes every month or so, but now he was telling us (with total conviction) that he was going to master the trumpet. Later my husband quietly told me, "Don't worry. This too shall pass."
But it did not and for the next several weeks we heard a lot about trumpets and his friends with trumpets. The fact that he stuck to the same topic for more than two weeks convinced us that he was serious about wanting to learn. We certainly did not want to discourage him from showing an interest in music. So we decided to make the investment and get him a trumpet, even though we were on a very tight budget.
Over Night Success? Not Hardly
After looking at all of our the choices (mind you, this was early internet years) we did manage to give our son a trumpet, which he happily blew on for about a month and not so happily for another month. After that, there was silence, despite our efforts to encourage him to play.
My husband then decided that he would learn to play, explaining that it had always been something he wanted to do. I think it had more to do with his inability to stand seeing our investment sitting, ignored in the corner. However, showing complete enthusiasm, he took a stab at it. That also lasted about a month and like many other things that end up as dust collectors, so did the trumpet.
Six Years Later
About six years later (out of the blue) our son showed a renewed interest in his trumpet, to the point of returning to his music lessons, playing daily and attending summer band camp. He later played in his school's marching band and loved it. Looking back, as difficult as it was to afford the trumpet, I am glad we did it. It contributed to his happiness.
Moral of the Story?
If you are on the fence about buying your child an instrument because of the cost involved and the fear that they will lose interest, my professionally untrained parental advice is to try to work it into the budget. Worst case scenario? When you hand it to them they'll say, "A trumpet? Oh yeah, I changed my mind. I really want to be a professional soccer player." Remember, you can always sell it.
In the article, "Cut the Cost of Musical Instruments," I offer tips on how to decide if you should rent or buy an instrument for your child and ways to find affordable instruments.

If your child wants to play an instrument, let them, but look for bargins. Either try renting or see if relative also played.
My son got his first Clarinet from his uncle. He went on to play the tuba, sax, trombone, etc.
But we were always able to find good quality pieces used or almost free. He also learned to repair them, which gave him added income in college.
And having to really work to learn to play was good for him!