how do you explain yin and yang to a 6 yr old?

ok just a few quick thoughts..... the boy bought his sister a little tinkerbell notebook in which she instantly had to start making "to do lists" we both thought it was so funny, where did she ever even get the idea of a to do list? she has had to schedule every minute of her day since friday! saterday so woke up at 6 and her first words were "mom get up we have to start checking things off my list!"
on sunday she was back up at 6 wanting to start her list.... you can see she scheduled time for a morning snuggle.... so then she jumps and wants to go on to the next thing, i said "star it is too early to get up on a sunday, get into bed with me and we can snuggle some more...." she fires back " "IT'S TOO LATE FOR THAT! i have check off the next thing...."
so i told her to find some thing to play on the bed, because i am not getting up...... she find her "opposites puzzles" now understand each puzzle only has two pieces, a straight road and a twisty road, an old person and a young person, a long rope and a short rope..... so when she has them all put together she starts holding up the sets and asking "ok mom which one is the opposite?" it was the beginning of a hilarious conversation! "star neither of them are the opposite, by themselves they just are what they are, together they are the opposites of each other...... my son laughed! "how do you describe yin and yang to a 6 yr old?" it is fun to have to the two of them together again.....! i love my babies! they are both so interested and thoughtful! life is good!