Music lessons are very good for children. They appear to help academic performance. Depending on the instrument, they can be pretty hard on parental headaches, but overall it’s usually worth it.
Organized lessons and practice requirements are good, but you can also allow free access to appropriate instruments. Kids love trying to make their own music. I wouldn’t suggest allowing them free access to anything you don’t want to risk being damaged, but it’s easy to come by cheap keyboards, drums, recorders and such.
That said, assigning music practice is a good idea. My oldest wants a harp, has saved the money for one, but has to show that she will practice before she buys it. This summer she will have to show that she’ll practice keyboard regularly before we order her harp.