What I'm telling our new scouts, for backpacking in Idaho (dry conditions, lows to the mid to low 20s, seldom get sustained rain) what to get is a 25 or 30 degree down bag, adult size. Here is why:
They all want to use internal frame packs. A youth internal frame pack doesn't have much room, and there is no way a slumberjack synthetic bag fits in it. So the bag has to be packable into a smallish internal frame.
30 degrees down is the lightest sleeping bag that packs into such a small space, and is adequate in warmth.
They may be youths now, but in 3 years they are going to be adult size or close to it. Might as well get one bag that will serve them into their adult life.
What I am going to do is buy 2 or 3 such down bags, and then sell than at cost to new scouts. I think it will save the parents money in the long run, but not having to upgrade later.
For colder weather, for one thing youths have quite a bit better internal heater than I do. They can add clothing to their 25 degree bag, to add a bit of temperature range to it. Most of our winter trips are car camping, or using a gear sled on the snow, so they can bring two bags, or extra clothes.