The continuing destruction of the traditional family is not merely tragic; as aided and abetted by government, it is both criminal and suicidal.
Why do young teens have babies? BECAUSE THEY CAN.
Babies are cute. Girls are designed to have babies and to want babies. Their teen years are when they are at maximum fertility. Given an infrastructure of support that allows them to have babies without unacceptable consequences, then they will have babies.
The only way to change this is to remove the supporting infrastructure entirely. If they had to support their babies by working 12 hour days in McDonalds, they would stop having babies, or at least try to acquire a stable husband first.
It also used to be that girls married young, but to older men in their twenties who had stable careers. Girls marrying older men is currently seen as "bad" by society.