A well trained scent dog makes it completely clear where the source of the scent is. If the scent came only from articles, then the dogs would have zero'd in on those articles only.
From media reports at the time, the dogs did not zero in on articles; they indicated on scent away from the girls' bicycles and Elizabeth's purse.
For whatever reason, I think the girls did make it to Meyer's Lake that day. I believe that all kids are basically good but they all get into mischief and do a little boundary pushing on occasion.
A lot of posters have said that Elizabeth would never get that far from home because her mother was not well. I've been thinking about that and what I wonder is how much the children knew about Heather's condition? They'd already had one bad scare two years previously; would good, loving parents like Drew and Heather draw a detailed picture of what was going on with Heather's health?
I don't think so. I think they would be more reassuring, along the lines of "Mommy's defibrillator needs a little tune up, so she'll be going to the hospital soon and then she'll be all better again."
Since Heather said the defibrillator has to be removed from her body, "fixed" then re-implanted, my guess is that it is going off when it isn't needed. I don't think there is any way someone could hide that from other people; it feels like a horse kicked you in the chest when it goes off. So their children probably knew that there was something going on with Mom's defibrillator but good parents would be reassuring and treat it as just a routine part of having one, nothing to worry about.