D.W.
Hi D.!
One of my favorite places is The Science Place http://scienceplace.org/info/aboutus.shtml
The entire downstairs is 2 year old fun- a giant sand box, a nature type room where they can go "in" a beaver den, see bees making honey, dress up, etc..., a water room (they provide waterproof aprons)... it is really awesome.
The Dallas Zoo is great- the kids zoo has a lot to offer little ones and the DART rail goes right to the entrance gate. Since it cost $5.00 to park the DART fare makes that very cheap. And most 2 y/o think riding the train is great!
Hope this helps!