I was in the same boat. Turns out that crossbows are all geared towards larger folks in that they have a pretty high cocking weight.
A simple law of Physics. A shorter string length and heavier tension will combine to require greater cocking strength. Still, it would seem a youngster, or even an adult for that matter, would be able to use the rope method with both arms and the foot as an anchor to set a crossbow.
It also brings to mind the same question as to the safety in giving a youngster a firearm. That is, why give them a deadly weapon they're too young to handle on their own? In my generation, a kid was given a firearm when they were old enough to carry and handle it safely It.