My sons were 3 and 5 on our first trip.
My 3 yr old loved:
Adventures of Winnie the Pooh
Tea Cups
Train Ride
Everything in Toontown
Carousels- both DL and DCA
Autopia
Buzz Lightyear Astro Blasters
IASW
No dark rides
Tarzan's Treehouse
Soarin
Grizzly River Run(4yrs old)
Mulholland Madness
Turtle Talk with Crush
Pressed Pennies-bring lots of quarters and pennies!
The M&M minis container works best
When my son was 3 he was afraid of most of the characters, except for the face characters. He is almost 5 now and is still terrified of Chip n Dale, nobody else just the 2 cutest chipmunks ever.
We just went at his pace, when he wanted to stop the stroller, we stopped and just let him enjoy the park. It was killing me becuz before I had kids I used to do DL Commando style, but I also had to learn to slow down and take it all in.
My most cherished souvinear is the silhouettes we had done on Main St.
Every time I look at them I smile.
If you can only afford to do 1 character meal I would suggest Goofy's Kitchen
It had more wow factor for my kids and the food seemed better than the other cahracter meal breakfasts.
Have Fun!