My son is a downhiller racer (not a boater
yet) boarding on moving up to the junior expert division. He races around the state on the Mountain States Cup circuit. Very cool race series for DH and XC from beginners to pro level racers.
Both disiplines require skill and fitness. However, DH racing at his level is like class V boaters in my book, you better bring your A game or you going to get a serious beat down.
He also teaches XC for SIMBA out of Boulder a great summer kid's camp and XC team mentoring program for kids learning how to XC. They also expose the kid's to some DH. He enjoys teaching XC and the workout, but the adreline and real skill is in ripping downhill, and hitting the jumps.
If you have a kid interested in mountain biking and you live in or near Boulder, I would highly recommend SIMBA. I can not say enough about the biking and life skills they teach young kids.
This weekend is the DH Nationals at Sol Vista. All the top racers will be there as this is also a World Cup Qualifer. The pros will be hitting 3 jumps in row, two at 40' each and last one, they will be going 40 to 60+' from what I have heard. If your interested, check it out.