Welcome back, Rachel -
Your 4 year old will have a splashtacular time onboard the Disney Cruise ship and you'll surely be watching his face and his reactions to the many magical moments that your family gets to experience onboard. The genuine delight (and sometimes accompanied by shrieks, screams and bouncing) are reactions that you just don't see anywhere else outside of the Disney Theme Parks and the Disney Cruise ships. These moments are priceless!
He will feel like he is transported right into Andy's room when he walks into the Oceaneer Club. He'll probably stare at all the Toys Story characters and if he has seen the movie and likes it -- he'll be even more mesmerized to actually see and touch the main characters.
Some of the port adventures are restricted due to safety regulations - and it's always safety first at Disney. There are plenty of rides and special areas around the Magic Kingdom, and when my kids were this age, they adored the many attractions that were geared more for their age.
Not just for your little one -- but YOU need a vacation too, Rachel. Use the
Youth Clubs when you are onboard. Your son will have an awesome time playing with his new friends, and the youth counselors are great with kids.
Wishing you a most magical first time voyage with Captain Mickey!
~ Dolly