I'm not so certain the first officer on scene was a Police Officer. Public Service Officers are usually non-commissioned uniformed employees of cities who do not have arrest authority. Now, they can detain and call for a Police Officer if they believe a crime has occurred.
As for the main story, yeah, hopefully everybody learned whatever lesson they should have. Again, we do not truly know what the scene was like. However, with what I do know about it, I do not think I would have approached it with full on charges and an arrest. I would have scolded the lady. Even if she got an attitude, I'm fairly certain I could shut her down with reason and facts.
Look kids get kidnapped and/or die everyday. I don't care how far she away she was, several things could have happened to that baby including kidnapping, another car smashing into the van, the baby could have choked on something and died, or even just slip out of the seat and break it's neck. You cannot leave a child unattended at all, even to walk 15 ft, it is just not safe.
But I guess it's all a moot point now that charges have been dropped. Oh well.