D.C.
There is a big cat rescue park in Wylie. I've not been yet, but we are planning a trip very soon (maybe today). My good friend took her little girl a couple weeks ago and said they had a great time. http://www.insyncexotics.com/
The Arboretum is always fun.
Texas Discovery Gardens at Fair Park http://www.texasdiscoverygardens.org/
I took my little one to the Dallas Zoo last week and was VERY disappointed. Don't waste your money. The last time I was there was probably 7-8 years ago, but I remember it being much nicer. They do have a children's area that's fun, but not really worth it. But the Ft. Worth Zoo is great!