First of all, of course, you should/would not make any changes without careful consultation with your child’s diabetes team. The degree of change of Lantus (insulin glargine) relative to an intermediate-acting insulin [such as NPH] will certainly be different patient to patient and that may explain the differences you have heard. I believe the manufacturer suggests taking 80% of the total daily dose of NPH as the new insulin glargine (Lantus) dose. (e.g., total daily NPH is 37 units; 80% of 37 = 29.6; give 30 units knowing that you will likely need to adjust).
The dose of short-acting insulin, be that Humalog or NovoLog, will most certainly change as you will change from relative “fixed” doses to a schedule and regimen whereby the dose of Humalog will hinge on the amount of calories (or typically the carbohydrate intake) consumed at that meal and/or snack. This type of insulin plan is often referred to as a basal/bolus insulin plan and can be done through multiple daily injections (MDI) or with an insulin pump.
Typically, your child will need to bolus for snacks, but your son’s needs may vary given his activities.
One should be skilled (or be willing to become skilled) in carbohydrate counting and must be willing to take multiple insulin injections daily (including at meals during the day -as when in school) and also be willing to, one several occasions, check the glucose not only before the meal but after the meal as well (to assure that your insulin-to-carb dosing ratio is appropriate). Some advocate two hours after the meal. Your son’s diabetes team should guide you.
I prefer to wait until after the honeymoon so that one does not get a false sense of security while honeymooning that one’s insulin-to-carb skills are good. (For example, if you under-dose insulin while honeymooning, the pancreas may “make up” the difference leading to an acceptable glucose thus giving you the sense that your ratio is correct when it may not be.) However, I do not think this is a deal-breaker, and your son’s diabetes team will likely guide you.
It’s hard to judge whether to use all three insulins without knowing your son’s activity, meal, and glucose patterns. It will require a bit of trial and error to find out what works best. While one can add a bit of NPH as you suggest, and as we sometimes will do, it does somewhat defeat the purpose of the basal-bolus, flexible plan. In addition, keep in mind that you cannot mix Lantus in the same syringe with other insulins. So now your son would be taking two morning shots.
Even though Lantus is now approved for daytime administration, I still prefer to give it at night. Some children seemingly are “fast-metabolizers” of Lantus. If one anticipates a once daily, 24 hour lasting dose, then it should not matter, but if indeed the child metabolizes faster than that, then a morning dose may not last leading to hyperglycemia at nighttime.
DS