A pistol caliber carbine would be just fine. I wouldn't expect my novice family members to perform well beyond 100 yards regardless of the weapon.
I would prefer something more like a .45 or .357, but .40 or 9mm would probably do the trick.
I do have a little reluctance about Hi-Point. My experience with their handguns was not thrilling but I've heard little negatives in regards to the carbines. Even if they are reliable, I still don't think they'd have the ruggedness of a military arm.
Excellent suggestion mcp1810.