T.H.
You can try the Lakewood Early Childhood PTA: http://www.lecpta.org/
Dallas Blooms will start at the Arboretum in early March. It has activities for kids on Mondays and Tuesdays: http://www.dallasarboretum.org/DallasBlooms/index.htm
The library in Northpark mall also has lots of kids activties: http://dallaslibrary2.org/branch/bookmarks.php
We have our daughter enrolled in a MDO program at a local church. Most of the kids in the program are ones she will be in school with in a few years.