Punishment is not the answer. As Tacitus said; the more laws, the more offenders.
When a young girl gets pregnant it is already too late for her to make an informed and educated decision about having sex. Before this happens, they (and the boys) should be aware and know the full and entire consequences of their actions and all the possible outcomes, including babies, STDs and all manor of other implications. It doesn�t seem to me as though many of them are and this should really be down to the parents.