I care for child who has a very similar story to your sons... all fine until having a little piece of mums peanut butter on toast.
Now just over a year later, it has not been a problem. We are very used to carrying the Cetirizine and EpiPens on us at all times and checking that toddler does not help themselves to any food products.
We are waiting for an appointment to have more tests done to see if he is allergic to anything else
Good, that will help you and the professionals involved in your sons care to develop a Allergy Action Plan and using a allergy ladder to introduce food identified by the tests (such as Egg, Dairy).
It might be the situation that he only reacts to peanuts and only if ingested. For now avoiding all products containing nuts is a good idea and also any products cooked in peanut oil. At his age you are not typically giving him nuts to eat, so it's more about avoiding him accessing food that adults have around him, especially at Christmas when nuts can be present.
Being young the vast majority of food he will eat will be made by you using simple ingredients or will be commercially available baby/toddler products which are clearly labelled with allergy information.
Try not to worry but do be watchful of things that are within his reach. Inform toddler group leaders that he has a nut allergy, just so they can make sure nut products are avoided... many groups will not have food containing nuts available anyway but good to double check. Make sure any carers are aware... babysitter, nanny, childminder, nursery... so they too can make sure he is not fed anything containing nuts.