As others have said, knowledge is most important, without it, gear is misused, or not used at all. This applies to adults as well as kids.

As far as getting scouts to carry the minimum required stuff, it seems, at least as far as I have seen, that scouts today rarely wear the uniform, and if they do, usually only the shirt. With the current popularity of "cargo" type pants, many, if not most, of the scouts will probably be wearing them, it should be pretty easy to come up with kits that they can stuff into one of those many pockets (that is why I like cargos myself). Won't be as easy to tell if they are "equipped" that way as opposed to a pack or fanny pack, but there are ways to work around that.

As far as whistles go, I have to agree that a pea whistle is not the best, but I was required to carry a pea whistle as a part of my uniform, and actually did it for the first ten years or so. A quality pea whistle (Acme Thunder, brass, highly polished in my case), will work. I have stood in the rain directing traffic for more hours than I care to remember, and never had it fail to work. In really cold weather you do have to warm it up a bit first, or it will become attached to your lips. But at least you won't drop it that way. Much better than no whistle at all...