D.,
My son has allergies to milk, eggs, wheat, barley, and nuts. We found out when he was one year old, although he showed signs earlier. I don't know anything about corn allergies, but with our extensive list of no-no foods, I do know how hard it is to find foods without those things. I recommend a visit to Whole Foods as they have a lot of items that are free of what you need. The staff is also very helpful. When we go to restaurants, I usually take some food for our son (now 3). Sometimes he can eat some things on the menu. He can eat grilled chicken (as long as I specify to the manager that it can't be touched with tongs that have touched bread, butter, or cheese) and fries if they are not cooked in peanut oil. When he was younger it was easier and we just took food for him, but now he doesn't want to sit still as much. Red Robin does a great job and they can give you a handout for all of their dairy free menu items. I just always ask for the manager, explain the situation, and they cook the food themselves. Also, the Food Allergy Network is a good resource. Some sections are free, others are available for a free. http://www.foodallergy.org/.
I only have one child, but I do babysit other children, and I've always just told him "that will hurt your belly" when he sees foods he can't have. He also can't touch them because he gets hives from touching the foods with his allergens. We spend a lot of time handwashing everybody in our house. He seems to know what that hurt your belly phrase means now and will tell me that when he sees food he knows he can't have.
He is sort of used to what he can have now. Even when I've found a specially made food from, like Rice Dream ice cream or a pizza he can have (which aren't bad tasting at all from the brands I have found), but he is so used to not eating them that he doesn't even want the new stuff. Like I found a great brownie mix on 123glutenfree.com and they are really good, but he wants none of it!
I think it has just become a part of our way of life. If we are somewhere that has cake,I make cake or cupcakes from the 123glutenfree website for him. He doesn't always eat much, but he can have Funfetti icing so sometimes he just eats the icing, but even if it is just that, he feels included. Same thing if we eat pasta, I just cook his gluten free noodles and he feels included.
Good luck with everything,
Kim