All are available from the Robert King Music Sales, Inc. , of from leading music store suppliers. In the first area, Physical development and conditioning, there are several stages. Younger players are still in the process of building and strengthening their embouchures. Basic lip slur exercises and lip flexibility studies are part of every brass player's growth. Younger players will need to take care not to overextend themselves.
Proper rest is essential.
Frequently young players don't rest enough and end up tiring themselves out more than building their endurance. More advanced players will be building and strenghening their embouchures too. They will be challenging themselves to play for a longer duration, increased repetitions, higher, lower, louder, and softer. I recommend using a metronome, especially with younger students. Control studies are very important in this area too.