When you have a toddler you have to keep an eye on them at all times.  You keep tiny things out of reach because they are curious about everything and want to put things in their mouth.  As a parent I was always scared of my toddler eating stuff he shouldn't, and I was always fearful of things like this story. 

I remember when E was younger and swallowed a penny. I was so scared that I had the doctor on the phone in 2 seconds. Luckily the penny passed in a few days, but I couldn't begin to tell you how I would have felt knowing that he had swallowed magnets.