There is a incredible amount of things to do. If your goal is to cram as much in as you can, then you will not be disappointed. Based on a 2 year old:
Six Flags Hurricane Harbor
Dallas World Aquarium
Ft Worth Zoo...way better than the Dallas Zoo
Perot Museum ( I haven't been personally, but heard it's awesome)
Ft Worth Museum of Science and History
U.S. Bureau of Engraving and Printing
Sea Life Aquarium/Legoland Discovery Center/Polar Ice House (all in the same mall in Grapevine Texas...plus there is a Bass Pro Shops next to it)
Ft Worth Stockyards...daily cattle drive down the middle of the road.
There is Six Flags in Arlington, but a 2yo in summer wouldnt work due to heat and ride height. The older kids would dig it
I have lived in both Dallas & Ft Worth for the last 23 years and I prefer Ft Worth to Dallas because it just seems that Dallas has a faster and busier pace of life and everybody's always rushing to get somewhere...plus traffic sucks BIGTIME.
Based on the destinations, Traders Village or Jellystone would mean less drive time