The training run by the Center for SafeSport is very clear: do not attempt to investigate in any way, including attempting to determine the coach's motivation or talking to the child: let people trained in interviewing children talk to the child, and remember that abusers groom the adults and community around the abuser in addition to grooming children. According to the Center's training, your steps are: report to police; report to the Center for SafeSport; tell the parents if you believe that's safe. FWIW, I'd recommend reporting directly to the Center for SafeSport rather than USAG. There's an online form for reporting directly to the Center or you can call them.
One of (many) reasons to report to the police is that you don't know what they know: maybe this is the first time the coach has done something like this or maybe they have other reports on the coach or other suspicions have been reported to them.
Please back-up the video and store a copy in one more than one (secure) place. Both the police and the Center will want a copy.
Thank you for doing this and for protecting the children.