Based upon everything I've read, Stitch is already off the list for our near-4 year old. I'd suggest reading the many, many reviews very carefully. Don't know if you ever experienced Alien Encounter, but I'll try to paint a picture for you:
- Each guest must sit in his/her own separate seat. It's literally a chair with armrests keeping the guests separate from one another. You probably wouldn't be able to do much more than hold your child's hand.
- A set of bars lowers onto your shoulders. It's not meant to be a restraint system so much as part of the attraction's effects. But it is quite intimidating and can also be painful.
- It's entirely possible that a small child could escape his/her chair, but the parent would likely find it difficult to follow.
- The room goes pitch black (or very nearly so) during the show.
- There are atmospheric effects in the nearly black room - water sprayed on the guest (I believe to simulate slobber with the new Stitch version). The shoulder restraint system used to bounce the guest up and down somewhat to simulate the alien moving around. Not sure if this is still part of Stitch.
Unless the Imagineers make significant changes to Stitch before its grand opening, it just doesn't sound appropriate for a small child to me.
Tower Of Terror, IMO, is in a bit different class. ToT is less psychologically intimidating and more physically intimidating. Kinda like trying to compare a haunted house (with the frights, blood and gore) to the intensity of a rollercoaster. I can certainly envision a child that would have little problem with thrill rides like BTMR or ToT, and still be scared senseless by AE/Stitch.
Dinosaur is a little of both--physical and psychological.
Depending on how the reviews read over the next few months, Dinosaur may or may not be higher on my own list than Stitch.
I don't want to come across as lecturing you on your parenting, because that couldn't be farther from the truth. You know your kids better than anyone else. That said, my final piece of advice would be to remember that if you rush kids into an attraction before they are ready, the response you get may be an immediate aversion to ANY thrill rides. Make sure you discuss with them up-front exactly what will happen and try to determine for yourself whether they are really ready for the experience.