Best played with a large group of kids but we have had fun playing this at family dinner times, with just four. It works with any age, but is better when the children are young.
Sit round in a circle. Youngest starts. He smiles his widest, silliest smile at everyone round the circle, trying to make someone else giggle or laugh. He gets a point for everyone who can't keep a totally straight face. After a while, he uses one hand to literally "wipe" the smile off his face, and hand it to the person next to him, and on it goes.
When the kids are little this game can cause much merriment, especially if you are playing with mixed ages. Not many little children can keep a straight face when their Granny or Grandpa is grinning madly at them!