A lot of kids I train have decided to specialize in one sport. That's okay. But I always encourage parents with kids under the age of 13 to play multiple sports.
Not just from a burnout or risk of injury standpoint, but overall athletic development and there are also so many different things you can learn from playing multiple sports. I believe all of these experiences prepare a young athlete to be even more successful when he or she decides to focus on only one sport.
Here's a great article written in 2016 by the Washington Post. It's called, Playing one sport year-round isn't smart, even for kids who want to go pro . It references a couple of studies showing how playing multiple sports is more beneficial in the development of young athletes than early specialization.
Many of the elite high school athletes I work with today were multi-sport athletes until they entered high school, and many of them have continued to play at least one other sport. For parents of young athletes, it's worth the read and consideration.