Take the kids and yourselves to a nice restaurant and enjoy the wonderful Puerto Rican food in Old San Juan! Or you can take a cab to the Condando district for dinner and a show. Surely one of the ship excursions include a show- usually a flamenco show.
Shows of that nature is usally ok for kids if it has flamenco or a cultural bent to it. But sometimes the shows are geared more to Las Vegas revues and probably those type of shows are not appropriate for kids. Many years ago my husband and I and our son,
then 13, went on a ship sponsored excursion to a hotel for dinner and a show which featured "Hollywood Legends" which we all enjoyed very much. Talented singers took on roles as Liza Minneli, Neil Diamond, Dolly Parton, Frank Sinatra and others. You
might look for something like that. Magic shows are also common features at some of the other hotels. Might try tapping into websites about San Juan and see if there are any shows like that-- might even be a schedule! Otherwise, I suggest when you arrive in port, go to the tourist office and pick up any info that might give you leads to evening entertainment. I'm sure the staff at the office will help you.
JanGail