The biggest problem with young flutists is how long they can play in one breath. Most middle school flutists cannot usually play for more than 1-2 measures in a breath before they feel that they need to take another breath. Needless to say, the flutist is left constantly taking breaths, which makes for a very “breathy” performance. Unfortunately, most music consists of 2-4 measure phrases which means you should not interrupt the phrase with a breath before it ends. If it is a slow song with 4 measure phrases, then the flutist will have a very difficult time trying to play the phases properly.
When I started studying with Warren Little (former principal flutist of The Atlanta Symphony) I was still struggling with phrasing because of my breath control. He suggested a daily exercise for me to begin working into my daily practice routine. First of all, I was instructed to set my metronome to 60. That is the equivalent of one beat per second. Then I would turn the metronome on and count to four slowing inhaling as I am counting. Then I would begin to play a low G (G1) at a mp level (moderately soft). The point of the exercise is to play it as long as I could. I found out that I could play the G for about 12 seconds. Then Mr. Little proceeded to do the same thing. As it turned out he was able to play the low G for almost a minute. I was blown away!
He then explained how to increase lung capacity. Always turn the metronome to 60 and start with the low G. After that wait 2 seconds as you take a breath, and then start again on A. Repeat, and go to B. Repeat. Go to C. Eventually you will go as high as you possibly can. In my case he had me go all the way up C4. That is the second C above the staff. I found out that the higher I played the less I could hold the note. He explained to me that is perfectly normal.
He had me practice that exercise every day. And guess what? After about six months I was able to hold the low G for over thirty seconds! Try it! You will be surprised how fast your body adapts and increases your lung power! Also remember that all physical activity will help to increase your lung power. Playing sports, riding bicycles, and swimming are wonderful and heathy ways to develop your lungs. Mr. Little was a swimmer. I try to run around 25-35 miles each week. Go ahead and give it a try. You will be pleasantly surprised! Good luck!