Hi Kneesey,
I'm a TA supporting a pupil with type 1 as well. Her parents are great in that they want her to be able to do everything her classmates do, and never want her to feel left out because of her diabetes. If she was offered birthday cake at school, I would weigh it out (as I do with her lunch) so that we can work out how many carbs there are/what the bolus for the treat should be. She is on a pump though, and I know it must be different if he is using pens. In any case, I'd have a chat with his parents about it - see if you can agree on a weight that his portion must be for a set amount of insulin, although I appreciate that it must be terribly difficult as he is so newly diagnosed.
In terms of sweets to keep at school, we have a treatment box. There are biscuits for if her BG is slightly on the low side or if we are going to do PE, and ribena as a hypo treatment. Apart from that, she eats the normal school snacks - as she has been diagnosed for years we have a long list of how many carbs are in each snack. Again, I'm not sure how any of this works without the pump!
Is he managing to tell you when he feels wobbly/might be going low or high? I've found it worthwhile to let the teacher know if she is one or the other - her schoolwork is definitely impacted by how she feels and how her BG has been behaving. If she is high, for example, she finds it very difficult to concentrate in class and so we either work in a quieter area or, if the hyper symptoms are extreme (she gets tummy aches, headaches and dizziness) we find the time to complete the work later. PE can be a lot to manage (especially after a 60-odd carb lunch as PE is typically on 'cake day') but we manage most of the time!
Please feel free to ask me anything - I'm not an expert by any means but I do know how type 1 can impact a child at school, and might be helpful somehow!