BOTH of these girls appear to be older than 8 and 10, not only in appearance, but in some of their behaviors (facebook, cell phone, texting, running away/missing). Lyric more that Elizabeth, but both certainly have been exposed to more criminal and dysfunctional family dynamics than the average child of this age. Considering this, I would expect them to engage in certain risky behaviors and activities earlier than other children.
I think back to when I was maybe 11 or 12. I remember riding my bike down a dirt road 2 miles from home to a "forbidden" field with friends, climbing a tree in the middle of that field and smoking cigarettes that my friends had stolen from her parents. We thought no one could see us and we did this frequently during one summer until several people reported to our parents that they had seen us (after getting my butt beat, I never smoked again-LOL).
My point is...if had we been abducted in that field, our parents would have probably been scrutinized for saying "they would never go there" when witnesses had actually seen us going there frequently. Potential abductors that lived nearby would have certainly seen us (would have been difficult to plan an abduction by someone that didn't live along our path because of the different times and days we went there). It would have been assumed that the bikes were "staged" by someone because we "would have never gone there".
IMO...I know "back in the day", kids tried smoking cigarettes. Today they engage in other risky behaviors at an early age-cigarettes, drugs, sex, vandalism, etc.
I still believe this had family involvement and not a random child abduction, but just thought I'd throw another scenario out there.