S.B.
Paradise Pond - it's off main street in Grapevine. Only open Thurs and Fri from 9-11. Get there early, when they are full they don't allow anyone else in. Costs $1 per person. Indoor bounce house, playscape, doll play area, car play area, kid rock wall, dress up areas and more.
Grapevine Rec CEnter- I am not sure if they still do it, but they used to open the gym for kids on Thursday mornings. It was $1 per kid. They had mats, balls, toys, and a bounce house.
N. E. Mall and Ridgemar Mall both have free indoor play areas. I like Ridgemar MUCH more, it's worth the drive for me.
Leapin' LIzards or Let's Jump - bounce house play areas. I think it's around $5. We like Let's Jump more, they allow parents on the equipment to help kids and there is no charge.
FW Museum- we got a memebership. It's great for cold or hot weather. They change out the exhibits often and the children's play area is a lot of fun.
Playgrounds...Free. We are fortunate to live in an area with LOTs of parks. Just go early before they get too hot.
Spray Parks. Free. Haltom City has one, but I think they are gaining popularity everywhere. Check with your local rec center.
CR Smith MUseum - $2 for kid. $4 for adults. Lots of fun airplane stuff to look at and touch. The staff was great. Right now they also have a CYber CHase (PBS math cartoon) exhibit. I took my 2 and 5 y.o. yesterday. The 2 year old didn't "get" the math concepts, but she had a great time playing.
Bass Pro or Cabelas - both of these stores have nice aquariums. If you look online you can find out when the fish get fed. It's free.
Library- free. Story time.