Is it possible that the parents left DeOrr with GGPA and Isaac when they went into town and then when they came back they couldn't find DeOrr? Maybe they didn't want to admit to leaving their child with two people who possibly aren't the best caretakers? I'm not sure how it could go from that to a massive cover-up, is the only thing. I would think the parents' concern over finding their son (and if someone harmed him, seeing that that person was held accountable) would override any fear of telling the truth that they left their child with GGPA and Isaac. I guess this scenario probably doesn't make sense.
ETA: Also, no scent of DeOrr was found, so I think I'll have to abandon this theory...