Can A Coin Pass Safely Through The Stomach Of A Toddler If Accidentally Swallowed?

Hi im worried about my 3 1/2 son, 5days ago i was NOT sure if he swallowed a small coin (15mm) he was eating and acting normal. Everytime I ask him if he ate the coin he just said NO. My question is that, can a small coin with that size of 15mm can pass in his stomach spontaneously? His poop today was color green. I might just be overthinking, please give me any advice.