I completely understand your concern. I would be too even if I wasn't traveling w/ a child.
But I think it's far too early to panic. This has been news for one full weekend. Felix is right, anything could happen between now and your sail date.
I don't think for one minute that any cruiseline will be docking in Mexico if this doesn't get better. The last thing they need is a ship full of sick people.
With any luck, this'll go away quickly and you can enjoy your vacation.