I would go to the ER at Celebration hospital.
There is also one very close on 535 just north of Crossroads. If you call front desk they can advise. Have been there 3 times over the years for kids, family and friends - always got in within 30 minutes and got the right diagnosis.
I feel for the kid as I had a similar problem whilst in college. Keep in mind - broken bones issues are fairly simple to diagnose and correct.
I was in total relief after going from splint to cast - so - I think you are wise to have it checked out.
While I am sure it will slow him up on vacation - this too shall pass. Head to
WalMart / Krogers and get a very long flexible and skinny (1 inch wide) spatula! The sooner the better! Cast + 3 days and I got the itches! The skin drys out and becomes 100% unbearable! It becomes more aggravating then any pain! That Spatula saved me! After my cast came off I returned our spatula to my mom - who promptly threw it away! Loved that thing - was a live saver!
Don't tell him this, but, I did not let the arm slow me down. Work, drove a shift, played Frisbee golf and it did not heal properly and had to be re-broken! To this day I can predict rain! He is a young boy and I was 21 - big difference his bones are still green. He needs to have fun - don't let it slow him down, but, don't let him be a crazy man.
Go DAWGS! BEAAAAAAAAAAAAAAAAAAATTTTTTTTTTTTTT Florida! Please scout out Erin G from UGA at the Liberty Inn at Epcot!
Good luck!