There is already written a lot about goalkeeper coaching and training
I still believe that you need to learn the young goalkeepers the basic skills very well and not rush with that.
Raise them left and right footed, raise them to bring the body behind the ball, catching the ball well.
Learn them to dive with the hands forwards the ball, attack it.
Please do not learn them to block a ball, this is a hype and is only for the goalkeepers who can do it on a short distance.
You see so many goalkeepers who try to block the ball when they too far away, also when they block they turning away so instead to close the gap.
They open a huge gap.
It is also important to let them train with the team, so they improve their football skills and work together with the players.
To educate them well you need patience and put in a lot of joy in the training sessions, beside that you need to put details in the training sessions.
For every age make a year plan and make that clear to the goalkeepers and try to stick to it.
Off course things will change during and you need to adapt, that will make you a good trainer.
I am always open for advice were ever i can, so if you want to know something or want to have advice then Contact me