Here are Dave Gage's sons, Brody and Alex, now called the Brothers Gage, back when they were 10 and 12 year old kids. This video shot in 2015, is an unedited take playing an improvised blues and country based jam and having a bunch of fun.
One plays rhythm beatbox harmonica while the other takes a solo. They are both playing a standard key of "C" 10-hole diatonic in 2nd Position (which is also known as "Crossharp"). They both learned to play harmonica around age 5 and now also sing, play guitar, bass, drums, and keyboards. The key to getting good is consistency. They still practice every single day.