The Passenger Locator form is currently not required for Spain and the Canary Islands if you are on a cruise. Antigen tests are required for unvaccinated guests 12 years and above. Depending on the length of the cruise, multiple tests might be required. You do not need to go on a P&O organised shore excursion to visit the destination and children do not need to be vaccinated to visit this destination.
Please see here P&O Cruises’ Destination Entry Guide.