Since you signed up for the Guzheng Society, it means that you or your children like it. If you say this is a school behavior, schools should provide musical instruments. Then, if the school provides musical instruments, students can't take them home to use. Learning guzheng to go home without practicing is equal to learning in vain. Therefore, whether you are practicing at school or going home, you need to buy a guzheng to practice.
If you have problems buying musical instruments, you might as well not report to the Guzheng Society. It is best to choose club activities acceptable to your family.