Hi,
I'm sorry I can't give you any advice on the 3 hourly feeding regime Henry is on as my younger daughter was 2 when diagnosed, and so past that regular feeding phase. It is probably a good idea though as most fast acting insulins peak at around 2 hrs and then tail off over the next couple of hours or a bit longer. But I think perhaps Humalin NPH is an insulin mixture (of both slow and fast acting insulins)? If so it is even more important that he feeds regularly.
As for the huge swings in BG - it may take a while to settle down. Really only trial and error will teach you how his carbohydrate intake and his insulin doses match, there's a lot of readjusting to do. And tbh even now (5 and 6 years on from diagnosis) we still get huge swings at times. It seems to me that some children are more easily controlled (BG wise!) than others. A regular routine of eating and insulin helps, as a family we are a bit chaotic which is not helpful! Perhaps it will be easier for you as your son is still so young and you can set up good habits from now about regular mealtimes and so on.
As for hypos. Yes they are a worry. When my daughter was diagnosed at two we found it very difficult at first to know, and tested a lot. I used to feel sorry for her tiny little fingers (still do!). After a while we got better at 'reading the signs' and could relax a bit, but even now I still get up often at night to check them both (and the older is 14 now!). All I can suggest is taking it in turns with your partner, so that at least some nights either one or the other of you is getting some unbroken sleep. It is really important that you do this and don't let yourselves become utterly exhausted.
You are bound to be distraught. I felt that in a way I was grieving for the healthy child I'd had before diagnosis, but as you say they are still the same little people really, and you will become used to a new 'normal' more quickly than you anticipate, probably. I think once you are home, and have been taken under the wing of a paediatric diabetes team you will feel less anxious and less alone. So hang in there, the next few days will pass, you will know what to do by the time you leave hospital, and gradually things will look brighter.
Sue