How old are your kids? Mine are toddlers - on rainy days, we go to the mall! You can go to North Park and throw pennies at the turtles and ducks in the little duck pond (well - not AT them), window shop at Disney, Lego, and Build A Bear, and then head up to the food court to share a kid meal and a Jamba Juice. Total cost: @ $10. If you have older kids, a mall trip would also be good, but a little more expensive. There is a movie theater and lots of teen shopping. And - the people watching at North Park is GREAT! However, if you feel unhappy seeing 12 year olds walking around in designer clothes with $800 handbags, better stay home...
Galeria has a 3rd floor toddler playground, and also an ice skating rink. I've never done the ice skating but definitely worth checking into.
The Science Place at Fair Park is also good and has an omni theater, a toddler area, and also an aquarium.
If its nice at all, I LOVE the Dallas Arboretum and so do my kids. Dallas Blooms has started, and I'm sure everything is quite beautiful. We have a membership so we go all the time - but NO FUN on a cold and rainy day.
The zoo is also good, and you can check - if you currently have a zoo membership it might also work at the Dallas Zoo. A koala exhibit is just opening this weekend and the Safari part is also very cool. If the weather is just a little overcast/cool, this would be a good option.
I always take all of my out of town guests to Chuy's (on Knox - just off 75) for local Tex Mex. Knox/Henderson area also has Wild About Harry's frozen yogurt, and one of the largest Apple stores in the country. We also always like to go to the Froggies toy store on Knox anytime we are in that area.
Have fun! And, I'm quite sure that even on a cool day, Dallas is warmer than Kansas!