My oldest DD has asthma & needs her quick-relief inhaler on hand...on our most recent trip to WDW (June 2013), I placed her inhaler in a quart-sized Ziploc bag with its prescription box flattened. This baggie then went into the bin with my other "gels, creams, and liquids" (less than 3 oz.). She also has eczema & when we traveled to WDW in Nov. 2012, I placed the prescribed cream in with my other "gels, creams, liquids" because it was less than 3 oz. to begin with. If your son's cream is more than 3 oz., put it in its own baggie with its prescription box flattened (or put it in a bigger baggie with his inhaler).
I have found children's Benadryl in tablet form, thus negating the need to search high and low for a liquid version less than 3 oz.. If he doesn't like tablets, pack a bottle of Benadryl in your checked luggage...cheaper than buying it at your resort's "convenient store."
FYI: You can pack pills in your carry-on and NOT have to remove them at security (so long as it isn't an obscene amount). I always carry travel sized: Tylenol, Advil, Benadryl, Zyrtec, Zantac, and children's chewable Tylenol in my carry-on (I am a walking pharmacy). I then pack "back ups" for said pills in my checked luggage.
As for your Epipen: place it in its own Ziploc baggie, which will need to be removed at security. If your Epipen doesn't have a medical prescription "pasted on," you might want to bring its original box and/or doctor's note describing your medical need for said item.
I hope my response wasn't too lengthy! and Enjoy your trip!