Sorry to hear how unwell your son is
@Helen12
Being ill when you have T1 is always really difficult.
The sick day rules that
@everydayupsanddowns has referred to are very useful.
It can be good to just have some rules to follow without thinking too much about it.
I use tonic water if I am vomiting. My levels are usually so high I am well clear of hypos so more keen to be carb free. If your son is in Multiple Daily Injections (MDI) or a pump and not eating he won’t need any Bolus (quick acting) insulin, but will need to keep a watch on the amount of background insulin he needs.
I hope that he starts to feel better soon