Re: Simple answer

"Yes, by informing children of risks ("just say no" is not informative enough) including the risk of manipulative and of physically abusive adults; "

All children still start at zero information and limited neurological capacity to receive it, at age zero. Deliberately created ignorance limits the abilities of children, but best teaching still leaves some limits.

There are risks from manipulative and of physically abusive children, too.

"and by penalizing adults for preventable STD transmission (even if the sex itself was consensual and not otherwise physically harmful). Although in theory I see a case for also raising the cost of causing an unwanted pregnancy (unwanted for the minor - this can be for a boy too, like with Vili and Mary Kay, although that one was wanted), it should also be low enough that it does not significantly hurt the capacities of the adult parent to provide for the child too."

If a preventable STD transmission occurs in consensual sex between two minors, should anyone be penalized?
Who should provide for a child with no adult parent?

An obvious and reasonable way to raise the cost of causing an unwanted pregnancy without significantly hurting the capacities of an adult parent to provide for the child is absolve minor boys of all responsibility to provide for children of adult mothers. This provides a financial deterrent against adult women getting involved with boys - yet leaves the mother at freedom to work to provide for her baby or find a stepfather.

But girls are bigger problem - an adult mother of a wanted child experiences physical discomfort and risks to health and life, and commonly gets paid child support for the child she wanted. How should an immature (early pubescent, just old enough to conceive) mother get compensated for bearing an unwanted child (although the sex had been wanted)?