I thought I would have great suggestions here (as a city parent of an almost 5-year old) but darned if every one of our favorite places wasn't already mentioned by the super-fast, super-insightful LTH community. I can speak from experience that Chinatown, Wishbone, the Garden, Greek Town, Mi Tierra and the Garden are all kid-tested and parent-approved.
Another unusual/interesting place might be something like Russian Tea Time on Adams between Michigan and Wabash. It's colorful, plush, exotic, a little romantic. It's perfectly located if the trip also includes a visit to the Art Institute.
Also in the Loop, the Atwood Cafe in the Hotel Burnham (the reno-ed Reliance Building at Washington and State) is a pleasant mix of fanciful decor and interesting but not outlandish food. The cuisine is upscale (but not over-the-top) regional American. Good, but not intimidating. And the building is truly beautiful.
If Italian is the order of the day, how about Taylor Street or South Oakley Ave ("Heart of Chicago")? Both are lovely, distinctive city settings, winter or summer. Everyone has their favorites in those neighborhoods. Ours are La Vita on Taylor and Ignotz on Oakley.
Finally, my all-purpose recommendation these days is Cuatro in the South Loop on Wabash. It's like something from Miami Beach, without the Floridians, New Yorkers and Quebecois. The decor is stylish, the food is nuevo latino, a good mix of the familiar and the adventurous, the desserts are awesome. It's upscale, but not too much so for a family outing with a kid who is not a terror. It's usually a wonderfully diverse crowd, the best the Chicago has to offer.
Best of luck and I hope you end up somewhere other than Rainforest Cafe.