Smiling faces light up the world.

Meaning: When people smile, their faces become brighter and they make the world a happier place.

Choice of Words: Smiling means having a smile on one's face, faces are the front parts of people's heads from the foreheads to the chins, light means to make or become bright with light, up means to move or cause to move to a higher position, the is used to refer to a particular thing or person, world is the earth and all its inhabitants.