I have not heard any regulation for spa (I know you need put fence for pool). Maybe there is some regulation but I am not aware of.
I do not think you are responsible if tenant kid fall into the spa as long as it is properly maintained. kid can put his finger into wall jack and got shocked. As long as you put switch board to all wall jack, it is not your fault. parents need watch their kid. the same reason for spa.
just my opinion, not from real experience.