I ate a 1p coin when I was a toddler, it came out rather more tarnished then when it went in!
My son ate a foot off Luke Skywalker when he was 4, he’s always had a habit for chewing, even in his primary school years he’d sit there with some action figure dangling from his mouth when he was working at his computer.
Docs told us just to watch & wait and lo & behold, it appeared the next day.
He still does it with plastic straws now (thank goodness they’re becoming extinct!) at the grand old age of nearly 30.
They’ll eat anything (daughter ate half an earthworm at 18 months). If it hasn’t obstructed his airway (and it sounds like it’s already in his tum) and it’s plastic, so pretty inert, keep an eye & watch for it in his nappy. Obviously, if he shows any signs of illness, discomfort or distress, seek medical attention.
With my electronics & first aider hats on, the things everyone needs to be very vigilant about and keep out of the reach of children are the small, round button batteries, like you might find in small LED light strings (I have some in my small wire lights) or toys at this time of year.
Swallowing these is a medical emergency & unfortunately there are children who have suffered catastrophic injuries (with some deaths I think). Chocking aside, the chemicals (lithium or cadmium, carbon monofluoride or cupric acid) react with saliva & stomach acid to form a strong alkali (akin to caustic soda).
There’s so many devices & toys that use them, especially around Christmas.
But a sliver of nappy sack? It’ll make a great story to embarrass him with when you meet his new partner when he’s an adult!