Stop by a Dick's, and check out the, "new", Remington 514. It's actually a re-branded Marlin XT-22Y. Single-shot bolt action, great feed ramp. (the lack of which killed the Henry for me)
It might be a little bigger than what you're after, even though it is considered a "youth" size. I have shot my son's, and it's actually a neat small-size rifle.
Two Weaver #12 mounts, and a Nikon 4X, have made it a very accurate 50yd gun. It hasn't been tested past that.
.my guess is they mean locking mechanism on bottom. All it take to lock the rifle is to push a button. It then takes a key to unlock it. I disabled it.
This must be an optional "feature," as the rifle I bought for my son, and all the ones we have in-stock at the shop, lack it.
The one other modification i made was to replace the front sight. I installed a high viz one which made it easier for the 10 year old to use peep sights.