Hummus

Wow, scary and strange. Like other say, it is likely that canned beans were once dried. So is there something in the canning process that negates the allergy? Or do you mean that the beans need to be fully boiled and soft? I agree that your son should just avoid beans until you figure that out. This allergy may change or lessen with time, which you can figure out with your doctor. I used to have all kinds of allergies that are now quite minor.

As others have wisely mentioned, please consult your doctor and/or allergist about this -- your son's safety is of utmost importance.

Why try to find a form of beans that your son can eat without symptoms? Since he already has shown a serious reaction to beans, it may be best to avoid them altogether. Sometimes exposure to a food related to one known to harm can bring up a reaction --- so even though he tolerates the hummus now, even that may cause a reaction in the future. A serious allergy/sensitivity should be respected.
(Thinking about his situation, I am afraid that all our good comments may not be appropriate. Listen to creamtea!)

All canned beans were dried beans at one time. It seems to me this is more a question for your allergist than for either us or your pre-school teachers (-she said, wearing her "doctors' wife" hat). Anaphylaxis is something to be taken seriously, as you no doubt know. It seems impossible to tell how a given manufacturer may have produced a given product, and the production method can always change.

Just to clarify, you say your son is allergic to dried beans. But what about dried beans that have been soaked and cooked--the kind of thing you would do at home? I am asking because if he has problems with dried beans that have been soaked and cooked at home, then I would be very careful about letting him have hummus unless you know how the beans were prepared.

To confirm what I said --
In Arabic the word hummus is used to describe the dish or just chickpeas by themselves. The full name of the dish is hummus bi tahina (Arabic: ?????? ??????) 'chickpeas with tahini'. Hummus is popular in various local forms throughout the Middle Eastern world. Its origins are unknown and are hotly debated throughout the Middle East. http://english.turkcebilgi.com/Hummus
So, although you can use other beans in a hummus recipe, it isn't -- literally -- hummus.
Falafel, on the other hand, is made from fava beans, or both, in Egypt. (Favism is a serious reaction to fava beans. I would suggest your son totally avoid them!)

As far as I know, hummus is always made with cooked chickpeas (traditionally). However, falafel is best when made with soaked, not precooked, chickpeas, so your son should avoid that.

Cannellini Beans I feel, even though non-traditional make hands down the best hummus. Some fresh garlic, quality olive oil, scallions or chives, an drained beans. Puréed to a smooth paste and you have a low fat delicious snack.

Canned Goya or Progresso chick peas (garbanzo) make excellent hummus.

I always used canned beans for hummus and it is very good

You could get canned garbanzo or make it from canned cannellini beans they are very creamy and they make a good hummus