No. Swallowing your own sperm is not harmful physically, although the emotional issues might be up for questioning.
swallowing sperm is harm less
It won't do you any harm.
If you're scared, don't do it. You don't have to. There's no harm to it but no real benefit from it either.
If you are female you don't have sperm. Only males have sperm.
Anyone can consume sperm, the question is whether you'd want to and who is feeding this to a twelve year old. It is highly nutritious, but, especially if the sperm is not the boy's own, the risks are that of STD's and sexual abuse. If your question is whether a 12 year old boy can make sperm, the answer depends on the stage of his growth in puberty; some boys will be able to produce sperm at that age, but I think most won't. That is a matter of time. In terms of legality, no. Sexual intercourse of any sort with someone that young is illegal in most countries.
Yes, the Arctic circle sperm bank has a high success rate.
No
their own sperm
No
No. It is normal.
No. Sperm contains protein and natural sugars that belong in your body.
Yes. Unless your son did something unforgiveable, then as his mother it should be him that you take the side of. There are lines a partner should not cross, and harming your own flesh and blood is one of them. Even if he were the boy's father I can't see why you would allow him to harm your boy. Don't let him harm your son now.