My 15 Month Old May Have Swallowed A Bit Of

My 15 month old may have swallowed a bit of seran wrap. The thin stuff that covers food. If he did in fact put it in his mouth, it was about 3 hours ago. He's eaten since then, nursed, and had a nap. He doesn't seem to be having any trouble eating and there's no weird sounds when breathing. How worried should I be? It's Sunday but should I go to ER? How long should I watch him for? What signs say I should go?