Passing on knowledge and making sure that it is acquired by others is not always easy.
We mustn't forget that each is different in terms of their learning pace, their understanding and their past experiences. The difficulty in teaching is to be able to see and know when the person in front of you is ready to move on to the next exercise. Let's not forget that taking your time is crucial to the long-term learning of any new skill. Even if an exercise is successful, that doesn't mean that it becomes automatic. Teaching requires patience and sometimes creativity. If an exercise is not understood, don't hesitate to vary the instructions, perhaps because the image used doesn't ring a bell with the swimmer, for example
To teach children, it's perfectly possible and even recommended to use a game approach. Some games may not seem like it, but they lead children to carry out a task that they might have refused to do if it had simply been asked of them.
Every child is different and likes different things, so don't hesitate to adapt to your child. You can create an imaginary world in which you invent a story. Anything is possible. Talk to them about what they like: animals, cars...
At the beginning, try to keep a certain stability in what you suggest, especially in what is successful but still difficult to achieve. When children repeat the same exercises or tasks over and over again, they know what to expect and become less hesitant (out of habit). Add new goals as you go along, an extra exercise, a new game. Bring in a new element, around a more stable and repetitive session structure.
Teenagers are not much more complicated than children, let's just say they have more different motivations. We'll have to find out which one. The game is still there, as are the challenges (being better than the other person), becoming stronger, impressing someone..
Find compromises, if he finishes a session he can choose an exercise he likes (for example speed, legs, etc..).
To teach an adult, you need to be able to explain the point of the exercises and give them a goal. Adults often prefer to have objectives, both in the short term (on an exercise), and in the medium or long term (succeeding in doing more length without stopping, for example).
Adults tend to think a lot, and therefore think about how to perform each movement. Be careful to stay focused on one or two technical aspects each time, the most important ones. Trying to think about everything becomes very complex and can lead to giving up or feeling like a failure. This is not the case; each element will be integrated little by little. And the more important a flaw is, the more difficult it will be to think about something else at the same time. Work on one element, integrate it, and as soon as it becomes easier, you can move on to another one. Don't forget to vary the strokes and therefore the technical instructions, to avoid monotony.