That was why we chose PR for vacation, we were planning on short notice and had not renewed our passports so that ruled out the other places we were considering, but Puerto Rico was fine because no passport is required or anything since it's a U.S. territory. So we got tickets for PR, had a great time, beautiful place. Of course as adults we had to show our IDs like normal when boarding, no ID has ever been required of our child, no birth certificate or anything, I've never heard of one being required before (unless maybe when you're going overseas? someplace that requires passports etc?).