The idea was to buzz the mouthpiece through the pipe (holding down corresponding "recorder" holes to simulate the resistance of the actual instrument). When enough air support was used the ball would shoot to the top of the plastic tubing. I can't for the life of me remember what they were calling the things, so I can't find them online anywhere, but all of the parts can be found at a hardware store to make them. It gives kids visual feedback of what proper airflow looks like.
I use them for 1-2 weeks when learning proper airflow in beginners. After that if they're using weak airstreams when playing all I usually have to say is "Your ball isn't hitting the top!" and they understand to support the air more.
Another thing I've found is that kids don't have a good concept of their diaphragm, so I do exercises with them (especially tubas) designed to teach them diaphragm awareness and control, and also teach them that their lungs are capable of holding much more air than they're used to moving.
Sip the air: (Teaches them that they can expand their lungs past what THEY think is possible.) Take a deep full breath. Completely full! Hold it. Now take another sip of air and hold. Take another sip. Another sip. Another. Hold it! Now let go.
Find the diaphragm: (Teaches them what their diaphragm moving feels like with an involuntary emergency breath.) Take a nice, easy, relaxed breath and hold it. Hold it for as long as you can. Close your eyes, stay relaxed. The more relaxed you are, the longer you can hold it. Your lungs will start feeling uncomfortable...ignore them, you can hold it longer. They'll feel like they're on fire...hold it longer. When you can't stand it any more, open your eyes, hold up all ten fingers, and tick them down from ten. You can go fast, but you HAVE to count them all down one at a time. When you get to ten, let the air go...your first breath in after that will be your lungs pushing the diaphragm out of the way to fill up as much air as possible. Remember that feeling, and try to do it on purpose now!
Blow the paper: (Teaches to focus the air stream and to support the air speed all the way through the breath). Hold out a piece of paper by the corner at arm's length. Take in a full breath (diaphragm!). Breathe out through your mouth, focus the air, and try to blow the paper flat. Try to keep the paper up and flat for as long as possible! (Also works with small flags and mobiles...added challenge is to keep the flags from dropping across multiple breaths, or to get the mobile spinning as fast as possible.)
Hyperventilate: (Teaches them to breathe in fully and out fully at high speed. Use once they understand how to take in a full diaphragm breath and to support the airspeed all the way through the breath). Take in a nice, full, relaxed breath, then blow it back out through your embouchure...make sure the air stays fast all the way out. Show me with your hand what your lungs are doing...hand extended away from your body out in front of you is empty lungs, hand by your mouth is full lungs. In between the air is either moving in or out. Now, faster in and out. Make sure they're full breaths, all the way in, all the way out. Faster. Faster! Now slow it back down...slower...one more, nice and relaxed...and how many of your are light-headed? Good, that means your brain is getting used to the kind of air it takes to play an instrument...
I'll do these breathing exercises with tubas especially for 2-3 weeks. Generally the smaller the instrument, the less time I spend on it. Trombones/baritones 1-2 weeks, trumpets 1 week. French horn resistance is so high that I usually don't spend that much time on air volume...more about air support to support a steady buzzing pitch. Oboe is similar, don't have to spend a lot of time building air volume.
Clarinets, take off the reed. Then tell them to play as loud as they can. Gets the air flowing. After a few minutes, put the reed back on, use the same airflow they were.
Flute, similar to tuba in terms of air volume and air support. Consider Pneumo pros to teach air speed to spin propellers (also teach air direction).