Can children at age 12 use this weapon also does it break easily?

You used the word "weapon" so you know it's not a Nerf type toy. As for letting a 12 year old use it, that depends entirely on the 12 year old and your parenting of him/her. If your kid is the type who would shoot the neighbors cat "just to see what it will do" then you shouldn't be giving your kid any kind of weapon at all. If you're the type of parent who would look the other way when the neighbor's cat got a crossbow bolt shot through it then you shouldn't be considering anything but Nerf guns. This weapon is about in a class with Wrist Rocket slingshots, which are also not toys. I do not consider BB guns toys if they have enough power to shoot out an eye. If you would trust your kid to safely handle a .22 rifle, a Wrist Rocket slingshot or a powerful pneumatic pellet rifle then you should be able to trust the kid to handle this correctly also. If not then don't give your kid this or any of those other weapons either.As crossbows go, this is a very tame one but that doesn't mean it's safe to use unwisely or by a careless person. A real hunting crossbow has a lot more force than this pistol type bow does. Users of "real" crossbows might call this a toy but it's not. I hunt with a serious crossbow and I would never consider something that does what this "little brother" does to be a toy. It's a weapon, it's just a light weapon but a weapon none-the-less. This little crossbow can kill or inflict grievous bodily injury. It has sufficient power to end or ruin someone's life so it's not something you should be deciding on by relying on answers to a question on Amazon.So the answer to your question is arbitrary and conditional. That is why you see some people answering your question "absolutely not" and some saying "yes, go ahead". Asking a question on Amazon is no substitute for exercising good judgement regarding your own progeny.

Could you leave it cocked and loaded for an extended period of time, say, in your car or house as a ready defensive weapon?

Technically, yes. It is better to use a BB gun instead - it's easier to conceal, it less likely to fire unintentionally, and can be fired repeatedly rather than one-and-done. If you are going to use this as your defensive weapon, it is better to cock it but not load bolt/arrow into it and keep the safety engaged - if it fires then, no harm can really result. Most importantly, check your local laws and regulations.Self-defense note: if your attacker is trying to attack you with a concealed knife, the best thing you can do is wear riveted chain mail (it actually isn't horribly heavy) - if someone wants to stab you, they aren't going to tell you "I'm going to stab you," casually wait for you to get to your car and shoot them. If your attacker is a road-raged person, you are in control o a multi-ton projectile called a car and they are outside. Keep windows closed and they can do approximately nothing.If your attacker has a ranged weapon, you don't have long to live (i quote multiple sources, "action is always faster than reaction").

Can I use scope on it?

You can it has a weaver style mount .I would suggest a reaction red dot instead as the distance you can shoot it really isnt long enough for a scope. I shoot about 15 yards with the sight it comes with and hit the center 99% of the time.

Does it come with instructions to put together and how to handle/manage it?

There is a youtube video that helps A LOT when putting it together. The instructions that come with it are not to clear on where to put a couple of small pieces, but the video showed it very well

ASIN	B079Y16M5V
Archery Draw Weight	80 Pounds
Best Sellers Rank	#66,519 in Sports & Outdoors ( See Top 100 in Sports & Outdoors ) #15,703 in Hunting & Fishing Products
Brand	Ace Martial Arts Supply
Brand Name	Ace Martial Arts Supply
Color	39 Arrows and 2 Strings
Date First Available	February 19, 2018
Hand Orientation	Ambidextrous
Item Package Dimensions L x W x H	20.43 x 7.25 x 2.18 inches
Manufacturer	Ace Martial Arts Supply
Material	Aluminum, Fiberglass, Metal, Plastic
Model Name	Pistol Tactical Crossbow
Package Weight	1.43 Kilograms
Part Number	101-39-1

Cobra System Self Cocking Pistol Tactical Crossbow, 80-Pound

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