Wow, your son sounds more 'nut' sensitive than mine.
As for when to use the epi-pen, my son accidentally ate a homemade cookie that had minced walnuts in it. The neighbor had told us they were chocolate chip, not chocolate chip with walnuts ... :/
He went in to an immediate reaction, and we did so many things wrong. His his throat got itchy, his face turned bright red, vomiting, hives. I wasn't home, told hubby to use the epi-pen, but hubby was hesitant. 'I don't know if this is severe enough for that.' He's vomitting, so it should work itself out. I convinced him to give him 1 tsp of liquid Benedryl. When he didn't throw that up after a few minutes, we gave him another dose. He was still feeling like he was going to vomit when I got home 5 mins later. We called the dr.
He said that since he had ingested it, we should have given the epi-pen right away, when the throat itching started. Waiting until the tongue swells and the lips turn blue, would have been too late. Giving him the liquid Benedryl instead of a pill is probably what saved him since we didn't use the epi-pen.
We rushed him to the ER (hubby didn't want to bother 911. Grrr.). They monitored him for an hour or two and sent him home.
I was so scared. So much doubt when the time to make the call was needed. I almost lost my son. :/ By the Grace of God I didn't.
As for playing sports, you will need to talk to the coach/team/friends.
1. Every player MUST wash their hands before playing.
2. Every game MUST use a ball that is new/monitored
3. You son should wear long sleeves and/or gloves to minimize contact.