I've had the same problem with my youngest daughters. Old-school revolvers with the thin round-butt grips are pretty much it until the hands get big enough for something like the Beretta .22's or the Walther. They are hit and miss hunting on the auction sites. If cost is not an issue, Ruger is making the sp101 in .22lr now. That's a fairly small length of pull that you can use in single action. A bit heavy for kids though. Mine like my lightweight Buckmark once their grip gets long enough to it. (your 10 year old, but probably not the younger ones).
9mm and 45acp are equally lousy. There's not a dime's worth of difference in REAL terminal ballistics. Get over it.