If memory serves, pennies are the most common object for young children to choke on, coupled by the fact that anemia makes them “tasty”. Perhaps we need to consider adding holes in coins to reduce that.
They said that most just pass though the digestive system, I was special
Would there be downsides outside of manufacturing cost and having to design with the hole in mind ?
It takes a long time before any of the other senses become mature enough to be (more) useful avenues of accruing information and parents can finally stop worrying about it.