Another nice one!
One trick you can try in regard to focus... the 350D should have a setting called "AI Focus" which tells the camera to try to keep up with a subject even as it moves in and out of focus. It is good to use for sports and capturing action. It also helps to if you have a lens with fast USM focus but play around with the AI and see if you can get some sharp action shots. Following pigeons in flight is good practice!
I can go to have others shots and try AI focus. The skate park is near my home, and as I send all the shots to the youngs, I'm sure that they will be OK, to do it again.