Hi there and welcome from me too. My son was diagnosed at the age of 15 a few months ago, and I agree with the person above, we were terrified at the thought of the first hypo. I had visions of him collapsing and us having to dial 999. Instead it was him just calmly coming to us, I grant you looking deathly white, but he had the shakes, said he felt sick and his body was telling him he needed glucose. I can't remember the specific figure now, nothing too drastic, but then he had been well into the 20's when diagnosed so was bound to feel odd when the levels dropped so much over the first few weeks. We were given loads of information at the start, but I do think that's the only area we were perhaps a bit misled, I certainly expected a full collapse from him, but touch wood, so far that has never happened. Hypos became quite a regular thing for a start, but now things have settled down a lot and we have odd spells of them, but never anything too drastic. We have had one or two 1.9s and he has still been standing and able to communicate, so though the first few will be a bit scary, it's not half as bad as you imagine.
Going back to school will be hard for your child. My son was diagnosed during the Christmas holidays. That was a bad time as no-one was around. We had to keep him home the first day back until I was sure the school were fully aware of the situation and had things in place to help him if needed. We had to supply a 'hypo box' for school with coke, dextrose tablets and cereal bars in, and our school nurse has a supply of my son's needles too, as he managed to forget to take those in with him one day and it was a nightmare getting some down to him that particular day, so she keeps a spare handful in her office now. The first few weeks back at school were a very anxious time for him and he did suffer from diarrhoea each morning for the first few weeks, which the professionals all put down to a stress response, understandably so.
Whilst you have the summer holidays, I would advise you to invite your child's close group of friends round, maybe one at a time, to start educating them a bit and take the mystery out of it before your child returns to school. They will rally round your child and become quite protective. You may get the odd one going a bit funny about it, but on the whole they are great. My biggest fear was teenagers messing about or perhaps pinching his stuff 'for a laugh' but it just hasn't happened. He is allowed to take a friend inside if he wants to when he needs to inject, though he is now very private about it all. School have also been very understanding too when in the early days I seemed to be phoning every other day either excusing his absense or asking advice. I never had any real contact with the school before, but they do understand your anxiety. It is hard for us mums saying goodbye and passing that responsibility over to other people, but you do get there in the end. Good luck!