TBH, I'm not "shocked" per se, amused, perhaps. Teenage pregnancies happen all the time, as do pre-teenage pregnancies, probably not in the UK though, but you'll see them all around Africa.
Don't see why everyone's getting so shocked about the boy's proclamation that he will take care of the baby. It's not like he's living out on the streets of a foreign country now, he'll do fine: he has his parents and his erm, the baby's mom. There was no other option after she got pregnant, and hence his perfectly cool reaction that he'll take care of the kid and they'll raise him. Does the boy have issues? I'll say that he won't be humping anyone anytime soon, neither will the mom.
Though I can imagine how freaked out that baby will be when it learns its dad was 13 when he had sex with his 15 year old mom.