When we went for the first time two years ago, I too mulled over what would be best to start my 6yr old twins (boy/girl) and my 8 yr old daughter. We were there at Xmas so we were following the UG touring plan. Since my 6yr old son was a bit nervous about going I decided to do Buzz first b/c he likes Buzz and he liked the idea of shooting targets.
We walked right on to Buzz....and he immed. freaked out!! To him, it was overwhelming...too much going on, bright flashing lights and sounds.
Now that he is older, I think he will be fine and he is even saying he wants to do Space Mountain. But if I had to do it over again, we would go for Aladdin, Dumbo, TTA. Maybe Peter Pan or Pooh, although I agree with the inside thing. He said he was afraid we would be trapped inside!
Jill