Relatively new to the world around them, kids don't seem to have a filter when they talk. They are almost always honest with their intentions, but they lack almost any idea about what is and isn't appropriate to say. Socially acceptable norms aren't really learned until later in life (if ever), and young children are eager to learn as much as possible about the world around them.
It can be insanely embarrassing if they happen to say something in public that's inappropriate, but it's almost impossible to get mad at them for it. Anybody who has raised children knows the feeling, but all you can really do is shrug it off to kids saying the darndest things. These kids below may just be curious, but the words that come out of their mouths are just too funny.