I think it is foolish to indulge in any watersport if you can't swim, and criminally irresponsible to take a non-swimming child. Use the time and money this trip would have cost to learn to swim, so that next time you can enjoy it in safety.

Sorry to be so blunt, but I know of people drowned in shallow water in similar circumstances. Everyone always thinks it won't happen to them. I'm afraid sometimes it does.