Hi Sarah @bonetje , nice that you were there to attend to your son - the good old location, location, LOCATION!
You mention two of the three factors key to diabetes management - you mentioned insulin and activity but made no mention of FOOD. Most days of the week, I take lunchtime bolus as I start to make my lunch and then eat and head out to the gym for a 90-120 minute “moderate” workout and I’m fine but I lower my pump to 60% basal by the time I finish lunch and keep it that way for 4 hours.
I’m assuming that the insulin administered was a meal-time bolus and if your son had his lunch following the shot he “probably” should have been OK. Now, a second thought: your son is not using a pump takes a long-acting background insulin [something like Lantus] once or twice a day. If this is the case, check with his medical care team and see if on days when PE follows lunch if he should take a smaller meal bolus.
I’m not a medical doctor, but from long experience I could offer some other suggestions for his insulin therapy. But in the end, it will all depend on your son’s body and how quickly his insulin begins work and how long it remains working in him - each of us is different.