3 easy questions
My appetite, tastes, and attention span are similar to that of a 12 year old..
Hot Dog: Superdawg (Well, or Wrigley Field.. if you can get into a game!)
Pizza: Lou Malnati's.. I didn't even like pizza growing up, but I would always be ok with pizza there. And if for some reason, you have a non-pizza eater on your hands, their other food is good.
(If the 7 year old is a girl, you might consider the American Girl Place, although I think their new store is nothing compared to the magical paradise it used to be. Also Navy Pier is kind of a bore, unless you see a show at the Chicago Shakespeare Theatre. You might see if you can catch one of the free shows at the Millenium Park Shell. Obviously the Art Institute, and it used to have a ok restaurant, but I believe it closed... also, I am not saying it is gourmet, but your kids might like Food Life at the top of Watertower Place--merely because they get to pick what they want.)
I agree with American Girl Place if a small girl is part of the family, but highly recommend that you avoid their expensive cafe that serves stunningly bad food. also, don't bother eating at Navy Pier. Everything there is also overpriced.
Instead I would second FoodLife in Water Tower Place for a lunch. It is always fun for kids and the food is pretty good.
Here is my standard advice to visitors re view: the observation decks now charge about $15 admission. The Hancock has a fine restaurant on the 96th floor (Signature Room) that does a decent buffet lunch for about $20 and the view is identical to the view from the observation deck as it's only about a floor different. So for the $5 extra you get the view and lunch. The Signature Room is quite expensive at dinner BTW.
The Hancock is right on the lake so you get a better view of the waterfront. But the Sears (which is actually called the Willis Tower now) has the new plastic floor you can walk out on, giving the sensation that there's nothing under you, and that is thrilling. Personally, I opt for the Hancock since you can get lunch thrown in.
For children I definitely recommend Sears/Willis, for adults I prefer the Signature Lounge at the Hancock and skip the observatory. Kids like saying they've been to the tallest building in the country, and the experience (and pictures) of being on the ledge can't be matched. The museum aspect at Willis is very child-friendly and the right amount of information to hold interest.
Old Superdawg beats Portillos but Portillos wins over current Superdawg.
Sears Tower's SkyDeck is hella-cool for kids, but I prefer the views from the Hancock (and you can grab a quick (not great) lunch at the 95th with no extra charge for the view).
Malnati's without a doubt.