Hi 007
A little bit of fill flash could do wonders.
As above, a fisheye is perfect for skating and bmx.
All 3 of your photos have a distracting background that is cutting the boys in half. Both the first and second pics are really good composition wise (except for cropping out a hand but, hey, $h!t happens) except for the backgrounds. Get down low so you've got nothing but sky behind your skaters but trying to keep as much of the bowl, rail, ramp, etc... in the shot if possible.
First pic as above (again), no skater wants a pic of themselves that close to the ground. A skater looking at this pic will be able to tell that dude in the pic got some decent height a few milli seconds later, but anyone else just sees a skater a couple of inches off the ground, so try to get the shot just a split second later.
You're never gonna get a good skate shot standing as far away as you were in the third shot.
Cheers
Buter