So the kids are guilty as fuck.
Apparently after she saw the flyer in the door, she opened the door, went outside to see if the envelope had fallen onto the porch somewhere. The kids had just finished putting flyers on each door on our side of the street and had done just the first one on the other side. They looked back, saw her looking around, saw her look at them, stopped going door to door, and booked it around the corner.
The cop said when he found them they saw him coming from a ways away, so probably ditched it. Something so small would be easy to just chuck somewhere. He also said they may have already decided they didn't want it so ditched it earlier. Oh well, can't do shit else about it.
The flyers are for a local carry out that does pizza/wings/subs as well. I was thinking of checking there, but the cop already stated they use a 3rd party service to distribute those flyers. Apparently the cops in this suburb are bored as shit because they were all over this like a swat team today. The woman who works dispatch was on the phone with my wife for a while as my wife basically told the whole story I posted in the OP.