Ok....I'm thinking that these are normal American kids....
As such...
You should not compound one mistake with another.
Mistake possibilities include:
Forcing the kids to marry
Forcing the girl to raise the child
Forcing the child to be put up for adoption
Forcing the girl to get an abortion.
Everyone, including the parents, have ideas as to what is most convenient for everyone...except nobody is making a plan for the baby or what happens next in the aftermath of a birth for all of the children involved.
It was for convenience that the boy and girl weren't supervised sufficiently to keep this from happening to begin with. I mean really...they aren't old enough for dating unsupervised in my world...
Then....both dating kids need some serious counseling. Sure they got hormones but they absolutely disregarded every warning out there and the morals of their community. There are some issues there needing attention. Especially with her....it WILL happen again if her emotional needs are not met.
What's being focused on is the obvious "problem" but not on the manner or reasons the parties involved made the choices they did. This is purely two sets of parents fault.
Not the kids who caused the baby....sure they own some blame but really? In today's culture? They don't know how to do much of anything else...which is why this happened.
Marriage only because of pregnancy is a Horrible idea and rarely works, and that includes for adults.
The fairy tale assumption is that the two will eventually learn to love each other and become happy in the long run. What is more common is resentment and bitterness between the two.
And, yes, having both parents around is ideal, but that's assuming both will be happy in the marriage and with being a parent. Otherwise you have two unhappy (at best) people tolerate each other and the example of marriage is still skewed to the child. And that will likely end in divorce anyways.
And at worst abuse will happen. Someone I once knew this happened to. They were young adults in church, got pregnant and pressured to marry. She had no real interest in a serious relationship with him (it was just lust) and it showed in their marriage. He could tell and made efforts to change her mind, but being pressured into a marriage made it difficult.
He began resenting her for rejecting him, and for losing out on the plans he had for his life and became verbally abusive. They had some more kids and he could be verbally abusive to them as well (though much worse to her).
Even though they stayed married for over 10 years she eventually couldn't handle the abuse and kicked him out.
It ultimately ruined her entire life, the abuse ruined her mentally and emotionally and she was never able to grow to be independent of his money, which he used against her.
Last we spoke they had been separated over 20 years and her life was still in shambles, as was she.
So, yes, the kids had a male and female in their life, but was that really for the best?
Her oldest daughter became selfish and pushy and easily disregarded others (similar to her dad), her son I'm not sure of, but he developed a close friendship with a homosexual and defending homosexual rights and her youngest, daddies favorite, got into self harm and drugs by the time she was 18.
They all resent their father and none of the kids will talk to him anymore. And they don't sound too close to their mother, either.
So marriage for the sake of the kids isn't, automatically, a good option if that marriage is bad.