As far as the bump and run, when I was a child, I got "bumped" by a car. I was riding down the street and an older gentleman in a HUGE car came out of nowhere and hit me (he was pulling out of his driveway). It was hard enough to knock me over (I had looked to be sure no one was coming first - always did). Luckily, he felt the bump and stopped. I had a few scrapes and bruises but my bike was fine. Just wanted to throw that out there - it could be possible to bump a bike and not cause remarkable damage.
What about bumping a bike with another bike? Like the perp runs into one of the girls, knocks them off their bike, then offers to take them home? Or, claims they live by the lake and offers to walk the girls to their house for a bandaid. Or even rollerblades - could run into them and pretend they (the perp) was hurt (could do this with bike as well), ask for assistance getting to car. Take RBs off, or if on bike, ask the girls to set their bikes down and walk his/her bike to their car for them. Then the perp has both girls by their car and could have taken it a step further by asking them to help them put the bike in the trunk/on the rack/in the back (if a van).
My other thought relates to the purse being discarded. What if the perps brought a puppy(s) or dog(s) with them and let the pup/dog loose, then pretended the pup/dog had escaped and called out for the girls to help them catch the dog. Once the girls get it, they ask them to help them back to their car. Or just being kids, maybe the girls just wanted to pet the dog/pup and the perp says they have to go but the girls can hold the dog for them and walk them to their car?
Just a few different things I thought of while reading today. All just IMHO, and all just random thoughts.