Is there a website that might have happenings listed for Cinco de Mayo? As far as wine tasting - it's funny how many wineries are 'family friendly' now though isn't that an oxymoron? If possible, I would recommend you change your reservation to a less -dependent area with much easier access to public transportation, and frankly, a better area to stay.
Federal courthouse in downtown San Diego.
Do you like theme parks? If you stay in Pacific Beach, then the ocean is right there so it's very convenient.