It could be that maybe, in the beginning, an accident did happen to Haleigh while the kids were left alone and she died. The family was afraid they would lose Jr. because of neglect. They thought they could convince LE that it was, in fact, a stranger abduction, no one would ever be the wiser; they would keep Jr. with no repercusions. Case closed.
Then when holes in their stories started popping up, more lies to cover for other lies, etc, it just got out of hand. It had all grown so big and more and more people involved, they started to realize that they had dug an even bigger hole, and would lose Jr. anyway, Ron would probably still go to jail, and all the others in the family who lied and helped cover up the "accident" would also go to jail too, which could involve the whole family, as well as the Croslin family...Then along came the drug bust to complicate things even more. Now they are just leaving well enough alone rather than add on even more charges for even more family members. I don't know...just thinking out loud again...