S.M.
Well now, you certainly have varying responses.
My question would be more about what kind of plastic it is? If it's the kind that is easily chewed and you can see teeth marks and it's pretty soft and small, I wouldn't worry. But if it's the kind of plastic that is hard and splinters and could be sharp, then I'd call his ped and see what they want.
I too worry about this with my daycare babies. I worry a lot more about things like watch batteries, pennies, magnets, etc. All kinds of objects do find their way out. But sometimes they get lodged, cause bleeding, and even death. So it's perfectly reasonable to be concerned.