United States OR America??

Since we moved here I have noticed that people refer to the U.S. as America. I never really thought anything about it until this past week. As you know, Jason went to the U.S. this week. At two separate times this week someone has asked Sofia if her Dad was in America and both times she said, "No. He is in the United States.". I thought this was really funny and have since explained to Sofia that it is the United States of America and that people sometimes call it America and sometimes call it U.S. and sometimes call it the United States. I'm not sure she really gets it at this point but I will keep trying to explain.