It's a very good point and I'm glad the parent raised it. But wouldn't you find it distressing if teenagers were regularly found with a teaspoon full of plastic in their stomachs?
There is a laxative product that is commonly prescribed to childhood cancer patients that is just polyethylene glycol. You take about a teaspoon of plastic micropellets and stir them up in a glass of water and drink it.
The PEG used for medicine has very short chain lengths, and I would be surprised if it isn't liquid or water-soluble, and not taken in the form of actual micropellets.
I think we'd be a bit more disturbed if teenagers accidentally ingested the teaspoon full of plastic whilst going about their daily lives and eating their regular diet, especially if the plastic wasn't designed in a way which made it easily pass through the gut.
We regularly find teenagers smoke behind the school (at least around here), we don't panic because of it.
That would say more about the teenagers than about usage of plastic in the modern world.