I was a pretty active shooter way before the age of 10. Every time my dad "bought me" a gun, it was made clear that it wasn't really mine, because I was a kid. That is, functionally, it would have been purchased for me, but it was still kept in my dad's gun safe with the other guns, and the only time I could handle it was at the range and for cleaning. To me that seems like a pretty reasonable approach, as it encourages safe handling and storage. As for why someone would give a gift like that, if the kid is into shooting, why not? I personally don't like the weird "pink gun" culture that exists (mostly for the same reason I don't like the mallninja stuff, either; a gun should be a gun and treated as such, not a violent fashion accessory), but it's a valid hobby for kids to enjoy. Also, for reference, a Ruger 10/22 is a low-powered semi-automatic rifle that's one of the main choices out there for teaching children how to shoot (among other things), due to its low recoil, cheapness, and wide availability. It's not an assault weapon.
I did know some other kids whose parents let them keep guns in their room, and I've always thought that was incredibly irresponsible.