Having recently found out in a serious, frightening way that my 20 month old son is allergic to peanuts, here is what I would say:
* Call your pediatrician A.s.A.p. and let them know what happened, and take him in to see the doc to make sure he isn't having any residual problems (breathing problems can be asthma-like, and if slight, can be hard for a lay person to detect).
* Have your pediatrician give you a referral to an allergist or immunologist, preferably one that deals with kids. If they don't know one, have them contact (or you contact) the closest children's hospital. You will get in quicker if your child's doc makes the appt, though.
* Get your son allergy tested so you know what you're dealing with (how serious the peanut allergy is and if there are any other allergies to be concerned about).
* Eliminate peanuts, and all tree nuts, and sesame seeds from his diet until you get him allergy tested. This means reading every label on every box or bag of food. I was surprised at how many seeming innocuous things have peanuts or tree nuts in them.
It can take several exposures to trigger a "major event" (the facial swelling and hives on the face are SERIOUS, btw!). Allergies such as you describe are not something to mess with. The next exposure could be even more serious (look for tongue swelling or excessive salivation or trouble breathing--those are all things use an Epi-Pen for and to call 911 and not screw around.)
Peanut allergies are also not something kids "outgrow." 80% of people who have a peanut allergy have it their whole lives, and it generally never lessens, and in fact can often get worse with each exposure.
Check out www.kidswithfoodallergies.org for lots more info.
Please feel free to send me a private message if you'd like. It can be a scary to navigate the uncertain, hazard world of food allergies....
PS- I forgot to add:
According to the pediatric immunologist (aka allergist) we see, Chic Fil A is fine to eat at. This is because the peanut oil is cooked (heated until it breaks down) so it's safe to eat. It's the raw, uncooked oil that is dangerous to those with allergies. So, since 99% of Chinese/Thai restaurants use peanut oil uncooked in some of their foods, these types of restaurants are off limits for us for family dining. But we can eat at Chic Fil A.
Also, the majority of chocolate contains traces of peanuts, as are commercial granola bars, so those are pretty much off limits for peanut allergic people. Also, items from bakeries (like a store bought cake) can be a potential hazard.