4p-11p Safe to do Old San Juan with kids

[FOURunderFOUR]

We arrive in port at 4pm. I read on the NPS website that Castillo San Cristobal and El Morro are both open until 6pm. Would we have time (assuming we dock on time and are able to get off the ship soon) to walk there and explore for a bit? There will be 4 adults and our 5 young kids (ages 15mos to 6 1/2 yrs). Our kids are used to walking a few miles, and we will bring the back pack carrier for our little one as I hear strollers won't really work here. Is it worth the effort? Is it SAFE to be walking around after dark in San Juan? Is there anything else we can do here this time of night with the kids? The food and rum tour sounded nice, but it is adults only. So unless we can convince Grandma and Grandpa to babysit (or maybe we will stay on board with the kids and let them go) that is out. Any other recs for a family with young kids?

 

TIA!