Ok...well, I hear ya, my youngest is 7, so not too far off. I find he's great with rides that spin and/or are fast...but rides with scary images are what bother him. That said, obviously, some things freak out my 7 year old that plenty of 4 year olds can handle and vice versa!
You don't have to worry about Suess Landing...Cat in the hat is not dark, has a couple of good spins..not scary. Caro-Seuss-el is a merry go round, no problem there. OneFish, TwoFish, RedFish, BlueFish is no problem, (save a few squirts of water!)
If those are fine (and they will be!), if spinning isn't a problem then Storm Force would be fun. And for a zippy kids coaster (we're working up to thrills here!) the Flying Unicorn. Popeye and Bluto will get you soaked, but isn't scary...kind of rapid, but very fun. Dudley DoRight will get you soaked, but can be scary because the drop is pretty steep (more than Splash Mountain). If all this is going well, Spiderman should be fine too...my youngest wasn't even a little scared of that a year and a half ago. Triceratops is fine, camp jurassic is fun, and make sure he spends time with the Mystic Fountain! My son is scared of Poseidon's Fury and Jurassic Park River Adventure (some scary dino's and a good sized drop). Take advantage of the play areas, they're lots of fun!!!
At the Studios...ET should be fine...Hanna Barbera (sp?) is a simulator ride but not scary...DO go to CuriousGeorge's play area and bring a bathing suit, he'll have a blast, as will the older kids!
Kong is pretty mild as far as scare factor...he's very fake, my son was terrified of it, but did it and went right back on! Jaws can be scary...sit him on the INSIDE of a row. Twister, forget it...Terminator would be pretty intense too. Back to the Future should be fine if he enjoyed Hanna etc. It's a little more intense, but not too scary. MIB has a giant bug at the end, some kids get scared but if you play up the video game aspect of it, he won't notice!!! Earthquake is no real big deal, the lights go out and there is some shaking and explosions, so work up to it.
Sorry this is so long...and I know I forgot stuff, but I gotta go!
Karen