Yes. Coins are the most common objects swallowed, and the peak age is 6 months through 3 years. Thankfully, most pass through without a problem. But some do get stuck, often at the sphincter at the bottom of the esophagus.
Yes. A single xray on a 3 year old can include abdomen, pelvis, hips. This is perfectly safe. A ct scan involves perhaps a 1000 fold more radiation exposure, and there should be a very specific indication for performing a ct scan....At any age.