No student will learn to play an instrument with any proficiency without regular home practice. They will fall behind and be frustrated. They will say "it's not fun" Of course it isn't, when you don't want to do the work.
Learning an instrument teaches children something that most classes do not cover. That is, that it takes time and hard work to accomplish goals. Instruments take years to master and hard work. There is NO short cut. That is a valuable, and even essential, skill to becoming a person who will know the value of hard work later in life. Music is something they can take with them forever. They can share it at home, in church, among friends, and someday with their own children. Help them stick to it. Help them remember. It will pay off in the end!