As far as other advice goes, I go to Universal a LOT with my 7-year old son (we are annual pass holders), so there are several places that would be really fun for your 3-year-old to check out:
On the Upper Lot, go through the entrance until you find an outdoor place called "Adventures of a Curious George." It is a playground for kids with water guns all over it. It's a fun place for little kids to run around and get soaked (bring a swim suit for your kid if you want since there is a changing area nearby, as well as extra pair of dry clothes for them and a towel to dry them off afterwards). There is also an indoor place, right next to that water playground, where kids can go to shoot plastic balls all around the room (great place to dry off too).
Secondly, on the Lower Lot, there is a little place called "DinoLand" that's perfect for your 3-year old to play. Quite a bit of walking to get to it though. It's right next to the "Jurassic Park" ride.
As far as other stuff for kids goes, there is a "Universal's Animal Actors" that's fun for little kids. "Shrek 4D" might be another fun one to take your 3-year old to, or even "Special Effects" show which is close to "Shrek." Just be aware that some attractions have a height restriction for kids (40+ inches), i.e. the Simpsons Ride, etc, so your 3-year old won't be able to go on those rides.
Best of luck.