There are lots of strange things to come accross when it comes to humans. This one is odd, but not uncommon i'd say. I must admit tho, he looks damn young (not 6, but 8 or 9)...
It's a hard decision to make. "Stop them" or not... in some way, if they really want to have it their way, who are you (parents, teachers, friends, etc) to tell them if it's ok or not? On the other hand... what the hell did i know when i was 13? Probably not a whole lot...
Personally i would say (without any bad intensions)... "bad luck, life ruined early". I mean, they are far too young to be grown up already... what about taking your time to be a child first... before having one?
And beside all that...
She looks like her age... but was interested in a boy who looks like eight... one or two years more and i'd almost call her a pedophile... yeah yeah, i just wrote that... go ahead and flame me if you like.
What really counts in the end is if they are/will be happy (especially the kid)... no matter how odd they look as a family right now. I guess it'll be their parents doing most of the work for the baby anyway (at least until they are out of school, etc).
Still... my first thought was (and still is): "Life ruined".