One thing I would recommend is to make sure that you don't exceed your or your son's abilities by diving in an overhead environment if you are newly certified. I don't mean to be presumptuous, but most new divers, especially kids, are probably not ready to dive in the cenotes, even with a guide. Snorkeling in one is an excellent idea.
But diving in them requires excellent buoyancy control and comfort/confidence with being unable to immediately ascend to the surface. While the cenote cavern zones don't require specialized training and equipment, they are not what most people would consider beginner-appropriate. There are exceptions, and you guys may be among those, but it's not the general case.