Playing music is just fun. It stimulates the flow of hormones. So playing music can activate positive emotions. Playing music can make you feel really chill. Of course, it can also make you feel the opposite of chill.
Playing music can improve your self-esteem. Playing certain songs with people gives you a feeling of accomplishment.
Learning to listen is a skill that will help a person forever. Being able to direct and maintain focus helps with a lot of things. There are many opportunities for people who can tune in and focus.
It should go without saying that kids who study music do better in school.
Apparently some kids only stick around for the music program.
Music helps kids be more humble. It also gives them tools to keep better emotional hygiene.
Kids usually get nicer after taking lessons for a long time. It depends on how much they enjoy it. I have seen it happen though.