 [ Symptoms ] my son had dtap polio chicken pox and mmr vaccines now can barely move [ Disease ] a quarter is quite big but i have seem them harmlessly pass assuming that he did indeed swallow a quarter short of an x ray a safe and inexpensive way to find out if your three year old has a metallic coin is with a metal detector you can rent one or find out if you have a friend who may own one if a metal detector can not get a signal he probably did not swallow it if he suddenly becomes constipated or vomits you may have to expose him to a very low level abdominal x ray    one view only and it would not be harmful