Hello J.,
The trip to Disneyland would be fun but he will enjoy it more and remember it more at a little older.
We just had my 3y/o granddaughter's party here at my house and mom and dad let me do it ( could be that I begged or am a party planner) we had the best SCAVENGER HUNT! We kept it in a explorer's theme use Deigo or Dora as your guide. I bought most things at the Dollar Store to keep prices down and we had them like you would an Easter Egg Hunt find different items-- flashlight, bounceing balls with colored glitter, bags of candy, horns, bubbles, story books ( for the child that was older I got a work book)and magnigying glasses! The kids spent hours checking out leaves and flowers under the magnifying glass and then they got to take all their treasures home!
If you use a pirate theme have bandana's ,I got at walmart in a package reasonable, items from the Dollar store and pirate candy coins and each child went home with 10 pennies thinksing they were kings. You can even get a large box to decorate as a priate ship-- we cut up old sheets for the sails but you could use plastic tablecloths from the dollar store as well and they have wonderful colors!! As for cakes I have found that cupcakes are a child's favorite even thought the adults might prefer something else. Feel free to contact me if you want any more information I would be happy to help. I believe it is the memories not the fancy stuff that one has at a party that makes the day special. For the next grandchilds party we are going to have the theme "Its a Bugs Life" and center it all around nature and are going to make a giant cupcake then hollow it out and fill it with gummy worms and let them have fun eatting it. So think about the number of children unless its family not to many becasue they burn out on over load and then get someone to blow bubbles and let them play in that or since its almost summer get a small pool and invite them to a beach party -- one child always wants a halloween theme so people come dressed up so that is always fun, one child is a Christmas baby which makes birthday even harder so we have a specail Birthday tree and have requested people send birthday greetings he got one from President Bush, and one from Al Gore once that hung on his tree!!! So enjoy and relax. Being my favorite topic I could go on forever!