Right next to the Museum of Art at Balboa Park is a hidden cafe that is an awesome retreat.
We ate there twice during our week long stay and were more than satisfied each time.
There is the option to grab a sandwich (on a small brioche style loaf) for $8 or for $10 you can be served a sandwich like the one seen above with a choice of side (green salad, pasta salad or fries). I think the sit down option is the much better deal. Add water with lemon and you've got a lunch for two - with tip - for $25.
The open air cafe was great for children as you didn't feel the need to keep them silent, and the tablecloths were covered with butcher paper that you could color on with crayons. Although the meals were served quickly, it did help to pass the time.
I highly recommend this cafe if you're in Balboa Park. The chicken salad sandwich on sourdough (above) is amazing and I'll be incorporating their secret ingredient (orange zest) the next time I make one at home.