What I'm keying on is the report that these girls made a pact. That's a whole different dynamic than having sex for thrills. What is it that made them get together, presumeably as a group or at least under the leadership of one or several and decide to have babies?
I would think that these girls realize that pregancy is not the end, that nine months after conception a human baby is issued and thus there is something more to this pact that has yet to be revealed. Their disappointment may hinge on the group timing, pregnant together, birth together, motherhood together. I don't think we should underestimate these girls and their purpose(s).
So, it would be very enlightening to see the results of interviews with these young women on their motives, their expectations, their alliances and so on.
It's not a sex thing, but a serious pact, a binding agreement, a covenant, between them to start something new or different.
This bears watching as it may, via the "grapevine," spread to other communities if young girls see something better than the present way of living.
I note there is no men in this equation, just women and babies to be.
Men may, in their view, be the problem with their lives and thus are useful only for breeding. Wasn't there a movie about this some time back?