I haven't adopted a child yet, but what options do you have with them?

Can they grow up?
If you don't play with them, do they become bad people?
If they get kidnapped, can you rescue them?
Can you train them to be a mage, assassin, archer, hunter, etc.?
If they can grow up, how long does it take?
Can they cook food or hunt?
Can they be killed by enemies that enter the household? (I doubt it considering that the game's rating would be changed to A, and it might be terrifying for some people to find a dead child's body)

Does anyone happen to know the answers to his questions? Do you have questions you would like to ask?

"Can they be killed by enemies that enter the household? (I doubt it considering that the game's rating would be changed to A, and it might be terrifying for some people to find a dead child's body)"

This is a definite no.

Can they grow up? Doubtful. It would take 6-8 years of game time, and they'd have to go thru adolescence.
If you don't play with them, do they become bad people? I don't know if they're bad... but maybe they'll be resentful, or not like you. Might even run away, but I doubt it.
If they get kidnapped, can you rescue them? Yes. There might also be an option to ransom them.
Can you train them to be a mage, assassin, archer, hunter, etc.? It would be cool if you could.
If they can grow up, how long does it take? Se above.
Can they cook food or hunt? Cook food, maybe. It might be part of their "chores".
Can they be killed by enemies that enter the household? No. Only possibility is that they might disappear from the game if they're kidnapped and you don't rescue/ransom them. You WILL NOT be able to see them dead without sicko-generated mods.