Good action and colors.
Yeah it's a tough situation. Funny how our eyes deceive. We think it is bright until we try to take a photo.
Fast lens with elevated ISO is the way to go. If your son will be into this for a few years, you might consider a faster lens. Bill, who used to visit here, decided on the 70-200/2.8 when he was shooting basketball with his A700. A decent range of focal lengths and reasonably fast. It's probably about the right lens for shooting in a gym. (There is probably a discussion here in the Tamron eqivalent for less money.)
PS: How did the little man do?