I've been teaching young musicians for more than 20 years, and I can say with confidence that very few children will practice if not directed to do so by an adult. (If your child does, count your blessings.)

If a child is to make any headway in learning a musical instrument, a parent (or other executive figure) must be involved. We parents function as our children’s external frontal cortexes, the function of which is to project future consequences that result from current actions. (Interestingly, the frontal cortex doesn't reach full maturity until a person's late 20s, so our services will be in need for at least a few more years.) To learn a musical instrument (future consequences), you have to practice (current actions). That relation between the future and the present is an immutable law of musical progress. Parents supply the long-range vision that children lack—we connect the present to the future—and without us, there would be very few accomplished musicians on this planet.

To practice effectively, a young musician needs a place to work, a seat, a music stand, a working instrument, engaging music, appropriate goals, and, most of all, someone to help direct the practice.