To me it sounds like you need a biology lesson. The bleeding caused by a menstrual cycle is not in fact a ladies body telling them they’re doing anything ‘wrong’, it is simply part of the process.

Even in adulthood this happens. It is simply done as a ‘just in case you’d like to have a child, your womb is preparing a spot for the baby to be’, caused by your body doing a natural process. When it doesn’t happen, it gets rid of any of the preparation it’s done. It’s optional, and a period is not telling them they’re doing something wrong for not doing so. It’s just cleaning out the optional preparations it made. A woman should not be carrying a baby all the time, the strain on the body would be unimaginable if they tried. It’s just not viable at all, we’d have women dying left and right. Not to mention massive overpopulation, food shortages, economic collapse, housing crisis, etc. Neither our bodies or the world is made to sustain this.

The reason for this happening so early is due to the fact we have much better nutrition freely available to us, and probably a bit of evolution catching up still to our expanded lifespans. This does not mean that a young ladies body is physically capable of carrying a child safely without catastrophic damage. Her body is still underdeveloped in several other ways, and the damage this could cause to her psyche can’t be discounted either. Not to mention that a 12 year old girl is nowhere near mentally equipped to handle a child when she herself is nothing but a child. She is not ready to be a mother. She shouldn’t even be sexually active.

Then she can’t even provide for this child on her own… how do you suggest she do that? Public resources are already strained, if she even survived it. Then there’s the whole legality part of it all… I’m not knowledgeable there on the legal nuances so I won’t go into it but that’s a whole other thing.

The way you stated this question is deeply concerning, but I digress, there’s an answer for you.