I get asked this question a lot from many frustrated parents.
I feel a lot of the answer comes in if your child is not enjoying the lessons rather than learning music itself. Ask yourself :
1) do they show interest in the instrument they are learning ? 2) do they love their teacher?
Changing either of the two is always better than just quitting music altogether. Music is such a rare gift to have and is one that so many people say they wish they had focused on more when they were younger, that if you can , I always think you should try all resorts before giving up.
Lessons need to be fun so you need to try have a tutor who is fun or perhaps changing the gender can help as kids react to different genders differently .
Trying a different family of instruments can help, and as it is a challenge, can help ignite a fire in your child again- say from a Flute to a Guitar.
That or you can change the lesson plan. If lessons have been very exam focused, a 6 month break of solely learning fun songs from pop stars they really like without any exam related work can be enough just to relieve a bit of the intensity and get your kids falling back in love with music.
Similarly if your child has not been doing any exams, they may enjoy the competition and focus that training for an exam can give someone.
I always think a little treat or sticker on a chart can work wonders for motivation.
Try all these things and if they don’t work, drop me an email on email@example.com- I’m sure we can come up with something else!