I see nothing inherently wrong with getting a 10 year old a .22 rifle. ASSUMING they aren't allowed to use it at any time without proper supervision and it's locked away when such supervision isn't available. Take away the mystery of guns, teach kids to respect them and you greatly reduce the chance of accidents happening.
I was 12 when I got my first BB / Pellet gun. I shot and killed a bird with it. I felt horrible. So I guess I'm not a sociopath.
Back on topic: I didn't watch the video, I'm a softy when it comes to animals. Which is odd, as I hunt, but I do it in a humane way. I.E. using the proper weapon for the job. Not shooting a damn squirrel with an air-soft pistol. These kids were old enough to know that what they were doing was wrong but "bloodlust" had them and they ignored it. 14 - 15 is well old enough to know what is right and wrong.
For those interested I hunt Coyotes and groundhogs. Nothing for "sport." I live on a farm and such animals are more than a nuisance as they can kill. Groundhogs killing via the hole they dig which will break legs and coyotes using the obvious methods. Depending on range, either a .410 shotgun or a .223 rifle.