Because they are children and children do stupid things.

One problem is that they look a lot like silver dragees, little silver sugar balls sometimes used to decorate baked goods. See e.g. http://www.fancyflours.com/category/silver-dragees for what they look like.

I am still cringing from the thought of someone biting down on one of those!

Because irresponsible parents don't watch their children like hawks. Instead they let them crawl around on the ground, unsupervised, eating shiny things. The very definition of misdemeanor child endangerment. It doesn't get prosecuted nearly as often as it should.

I'm going to take a shot in the dark and guess you don't have children. It is simply impossible to watch them that closely 24 hours a day.