This is actually a game that my husband and I play when one of us is feeling really down, but it also translates well for a kids activity.
The rules of this game are simple. The first person says, "I love you because" and then says why they love someone.
The second person responds with "I love you because" and continues the same as the first person. This can go on and on and tends to move past the physical aspects of loving someone fairly quickly.
Here are some examples:
I love you because you make me laugh.
I love you because you are my sunshine.
I love you because you make me feel safe.
I love you because you giggle a lot and that makes me happy.
I love you because you are silly.
I love you because you are kind.
I love you because you are eager to learn new things.
I love you because your heart is beautiful.
I love you because you work hard.
There are truly an infinite number of answers that could be given in this game. The trick is to try not to repeat everything that your spouse or child or playmate says, which after a while can be much more difficult than it sounds.
And as a bonus, you could even use this game after your kids have been fighting and you want to remind them that they love each other, not hate each other. It would also work well in the car on a road trip since you don't actually need any materials to play the game.