Can I just say (haven't seen the prog) that the methadone thing can be a red herring. My dh takes it as a pain killer (I'm not joking, this is really true) - we have (fortunately) zero SS involvement in our lives. Being on methadone doesn't make you a bad parent, although I would question the set up when both parents are on it.
Obviously giving your two year old methadone is an entirely different matter We are extremely careful with the methadone in the house as we have no way of preventing ds seeing dh take pills (as per advice at the baby clinic) so he has to get used to it. But it is in a locked container and as ds gets older we will take more and more extreme measures to protect him from it, it's a terrible worry