[Spoilers] Question about Shinsekai Yori

Okay so I just finished it last night, and I couldn't help but wonder how the monster rats were able to get Mamoru and Maria's kid. From what I understood, Mamoru/Maria ran away together somewhere far away. Once Satoru/Saki found this out via the letter, they decided to report back to the village that they had died in an avalanche. Squealer told them he would take care of the bones for their bodies so their deaths would be believable.

So later in the show Tomiko tells Satoru/Saki that the bones they had found were in fact from Mamoru/Maria, verifed by their DNA. SO does this mean that, instead of running away together, Mamoru/Maria were living with the monster rats in order to hide? Or did the monster rats somehow kidnap them and kill them to use their bones as the evidence? If that's the case then how were they able to get Mamoru/Maria's kid? It takes at the very least 9-10 months to have a kid, and I'm assuming it didn't take the people who went looking for Mamoru/Maria's body 9-10 months to find them.

Did I miss some explanation? Am I making this way more complicated than it actually is? I did finish the last half over about two weeks so it's entirely possible that I just flat out forgot a scene where they explained this or at least gave an idea of what happened. Great show btw.