Hi Jose!
The run/walk/run interval is a great way to race! It's what I do, and also what Disney's official trainer,
Jeff Galloway, endorses. You will also see plenty of people that will walk the entire time, and that's OK too!
The pace requirement is a 16 minute/mile pace. That is really just a brisk walk. There are "sweepers" that follow along at the very end of the race at that pace. The good news is that unless you start very last (and that would be in the stroller division), you will automatically have extra time. The pace sweepers will begin at the very end of the race, so you may already have a 10-15 minute head start.
It's a good idea to train at about a 15 minute/mile pace just to give you some extra time to stop along the course for some fun Disney pictures!
The Family Fun 5K's are very laid back and lots of fun! You will do fine! Please let me know if you have any other questions.