Man, when I was in the Boy Scouts the only guns we ever got to shoot were Ruger 10/22s.
If you could find the old Ral Partha Colonials, I'll bet they'd work. They're pretty much exactly 25mm scale, so they'd look a bit like kids next to today's 28-30mm stuff. I'd look for Boers on foot, they'd probably have the right kind of hat, and you could then just convert them to knee socks and shorts if you cared to.