I also highly recomend Confisco's for table service, but you should know there are many indoor air conditioned sit down dining options in every area of both parks, one is never far away. Most of them are cafeteria or fast food style, where you take a tray and select from the constantly replenished hot and cold counters or you give your order to the cashier and step up to the counter to be given your order to carry to your table. You'll find your basics here: pizza, burgers, fries,etc.
Some of the places offer more unconventional options like chinese, tacos, meatball subs, and more. Our favorite in IOA is the Burger Digs in the Jurassic Park area. We like to eat on the balcony, where it remains cool even on hot days. I do NOT recommend the chinese food at the Cartoon Lagoon Cafe or the Meatball subs at the Marvel Cafe.
At Universal our favorite is the cafe near the Back To The Future ride. Here I DO recommend the Chinese (very good hot sour soup) and Italian cuisine. They also have TV monitors all around the place playing clips of classic Universal movies, and for some reason this place always seems less crowded than the others.
One more place I like is not indoors but does provide picnic tables with umbrellas and worthwhile if you love fish is a seafood stand near the Amityville area. I am not a fan of fried food but I do love shrimp and scallops and the shrimp and scallop basket I got there was really great, crisp light breading, tender not overcooked on the inside, and not greasy at all.
For desserts IOA offers Cinnabon & Funnelcakes ( both outdoor seating) and here again we prefer Universal which has the Boulangerie near the front gates for sandwiches and desserts or if you really want to indulge a wonderful pastry shop between the New York and Amity areas. Both offer limited indoor seating and shaded outdoor seating.
There are also dozens of street vendors offering snacks, cool drinks, and fresh fruit.
Hope this helps!