My 10 mos old swallowed a triangular piece of a plastic fountain drink lid about 1/3 of an inch. no swallowing/ breathing issues. will it cause probs?

Possibly: If he truly swallowed it, it will probably be okay. It's pretty flexible and it should come out with his poo. However, notify his doctor in the morning. Also, watch for breathing problems or wheezing, as this could be signs that he inhaled it instead of swallowing it. And try not to feel too guilty, most moms have been through something like this (including me).